Euornithes sensu Sereno, 1998
Definition- (Passer domesticus <- Sinornis santensis) (modified)
= Euornithes sensu Longrich, 2009
Definition- (Passer domesticus <- Enantiornis leali) (modified)
= Euornithes sensu Turner et al., 2012
Definition- (Passer domesticus <- Cathayornis yandica)
Diagnosis- (proposed) caudal zygapophyses reduced (absent in Yanornis and Ichthyornis); tarsometatarsus fused distally.

Jiuquanornis Wang, O'Connor, Li and You, 2013
J. niui Wang, O'Connor, Li and You, 2013
Early Aptian, Early Cretaceous
Xiagou Formation, Gansu, China

Holotype- (GSGM-05-CM-021) furcula, sternum (28.9 mm), sternal ribs
Diagnosis- (after Wang et al., 2013) U-shaped furcula without hypocleidium; short, imperforate body of sternum; small lateral processes on sternum; lateral trabeculae distally expanded medially; elongate intermediate trabeculae, equal to lateral trabeculae in distal extent; V-shaped xiphoid formed by short, fused medial trabeculae.
Comments- This specimen was first described by You et al. (2010), then redescribed and named by Wang et al. (2013). Both used versions of O'Connor's analysis to recover it more derived than Archaeorhynchus and Patagopteryx, but less than Carinatae sensu Chiappe.
References- You, Atterholt, O'Connor, Harris, Lamanna and Li, 2010. A second Cretaceous ornithuromorph bird from the Changma Basin, Gansu Province, Northwestern China. Acta Palaeontologica Polonica. 55, 617-625.
Wang, O'Connor, Li and You, 2013. Previously unrecognized ornithuromorph bird diversity in the Early Cretaceous Changma Basin, Gansu Province, Northwestern China. PLoS ONE. 8(10), e77693.

Parahongshanornis Li, Wang and Hou, 2011
P. chaoyangensis Li, Wang and Hou, 2011
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China

Holotype- (PMOL.AB00161) eight cervical vertebrae, dorsal ribs, synsacrum, incomplete scapula, coracoids (14 mm), furcula (~13 mm), sternum, sternal ribs, humeri (one partial; 29 mm), radii (one partial; 26 mm), ulnae (one partial; 27 mm), radiales, ulnares, metacarpals I (3.4 mm), phalanges I-1 (7 mm), manual unguals I (3.7 mm), carpometacarpi (II 12.3, III 11 mm), phalanges II-1 (6.8 mm), phalanges II-2 (8.2 mm), manual unguals II, phalanges III-1 (3.2 mm), phalanges III-2 (1.3 mm), ilia, pubes (24 mm), ischium, femora (24 mm), tibiotarsi (38 mm), fibulae (20.7 mm), metatarsals I (3.2 mm), phalanges I-1, pedal unguals I, tarsometatarsi (II 20.3, III 22, IV 20.2 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers
Diagnosis- (after Li et al., 2011) coracoid elongate (length/distal width 2.3) (also in Hongshanornis); furcula anteroposteriorly compressed proximally (also in Yanornis); deep groove along clavicular symphysis (also in Yanornis); fibula close to half tibiotarsal length( also in Longicrusavis).
Other diagnoses- Li et al. (2011) listed other characters in the diagnosis as well. A U-shaped furcula, elongate sternum, xiphoid sternal processes, short posteromedial sternal processes (which create two pairs of posterior excavations), distally expanded posterolateral sternal processes, anteriorly extensive sternal keel, subequally long metacarpals II and III, straight and slender manual phalanx II-2, opisthopubic pelvis and a pubic boot are primitive for ornithuromorphs. The forelimb is also short in Patagopteryx, Hongshanornis and Longicrusavis. Manual phalanx II-1 is also short in Yanornis and Gansus. The tibiotarsofemoral ratio is also high in Hongshanornis, Longicrusavis, Yanornis and Gansus. The tibiotarsus is also slender in Hongshanornis, Longicrusavis, Yixianornis and Gansus. The tarsometatarsus is shorter in Archaeorhynchus, Jianchangornis, Patagopteryx, Longicrusavis, Yanornis and Yixianornis.
Comments- Li et al. (2011) referred this taxon to Hongshanornithidae based on the U-shaped elongated furcula and short forelimb. The former is also true in Archaeorhynchus, Yanornis and Jianchangornis. The latter is also true in Patagopteryx. It is here retained as Euornithes sensu Sereno incertae sedis, until included in a phylogenetic analysis.
Reference- Li, Wang and Hou, 2011. A new ornithurine bird (Hongshanornithidae) from the Jiufotang Formation of Chaoyang, Liaoning, China. Vertebrata PalAsiatica. 49(2), 195-200.

Archaeorhynchus Zhou and Zhang, 2006
= "Archaeorhychus" Zhou and Zhang, 2005 online
A. spathula Zhou and Zhang, 2006
"Archaeorhynchus spathula" Zhou and Zhang, 2005 online
Late Valanginian-Middle Aptian, Early Cretaceous
Yixian Formation, Liaoning, China

Holotype- (IVPP V14287) (subadult) skull, sclerotic plates, mandibles, ten cervical vertebrae, several dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, sacrum, few caudal vertebrae, scapulae, coracoids, furcula, sternum, sternal ribs, humeri (53 mm), radii, ulnae (56 mm), radiale, ulnare, carpometacarpi (25 mm), phalanx II-1, phalanx II-2, manual ungual, ilia, pubes (36 mm), ischia, femora (37 mm), tibiae (42 mm), fibulae, astragali, metatarsal I, tarsometatarsus (20 mm; one partial), thirteen pedal phalanges, seven pedal unguals, body feathers, remiges, gastroliths
Diagnosis- (after Zhou and Zhang, 2006) premaxilla toothless (also in Ichthyornis+Passer); maxilla toothless (also in Aves); dentary toothless (also in Longicrusavis and Carinatae); premaxillae broad with slightly rounded tips; dentary spatulate; strong longitudinal medial ridge on dentary dorsal to Meckelian groove; pointed omal tips of furcula (also in Yixianornis); forelimb elongate (humerus+ulna / femur+tibiotarsus ratio of 138%) (also large in Ichthyornis- ~176%); tibiotarsofemoral ratio 1.14.
(proposed) nasal process of premaxilla does not extend to orbit; quadrate without even incipient division between dorsal condyles; cervical centra amphicoelous (also in Gansus and Ichthyornis); caudal vertebrae unfused distally (ontogenetic?); distal coracoid laterally convex (also in Yixianornis); brachial fossa absent on ulna (also in Patagopteryx); muscle impression along most of ventroposterior radius surface (also in Ichthyornis+Passer); anterior cnemial crest present (also in Longicrusavis+Passer); tuberositas retinaculi extensoris tubercle absent on anterior tarsus; m. tibialis cranialis tubercle on metatarsus absent (also in Patagopteryx).
Other diagnoses- Zhou and Zhang (2006) also included the elongate foramina and grooves on the lateral dentary as a diagnostic character, but this is correlated with the lack of teeth. The broad sternum with deep posterior notches and elongate posterolateral processes are symplesiomorphies shared with enantiornithines. The character "hindlimb shortened" is already covered in forelimb/hindlimb ratio and tibiotarsal length. Metatarsals II and IV of Patagopteryx, songlingornithids and Apsaravis are also nearly equal in length.
Comments- This taxon first appeared as a nomen nudum OTU in Zhou and Zhang's (2005) online matrix, though it did not appear in their cladogram. If the matrix is run in PAUP, Archaeorhynchus forms an unresolved polytomy with Hongshanornis, Liaoningornis and more derived ornithuromorphs (Apsaravis, songlingornithids and Ornithurae sensu Chiappe). This is the same as the published tree in Zhou and Zhang (2006). In both papers, Patagopteryx was coded but excluded for no stated reason, yet emerges as the most basal ornithuromorph when the matrix is run with it.
References- Zhou and Zhang, 2005. Discovery of an ornithurine bird and its implication for Early Cretaceous avian radiation. Proceedings of the National Academy of Sciences. 102(52), 18998-19002.
Zhou and Zhang, 2006. A beaked basal ornithurine bird (Aves, Ornithurae) from the Lower Cretaceous of China. Zoologica Scripta. 35, 363-373.

Chaoyangiformes Hou, 1997
Definition- (Chaoyangia beishanensis <- Passer domesticus) (Martyniuk, 2012)
= "Chaoyangidae" Hou, 1997
= Chaoyangithiformes Zhou and Zhang, 2006
= "Chaoyangornithidae" Zhou and Zhang, 2006
Comments- Hou (1997) erected Chaoyangiformes for his new families Chaoyangidae and Songlingornithidae within basal Ornithuromorpha (his Ornithurae). As noted below in the Songlingornis section of the comments, there are no synapomorphies that suggest grouping Songlingornis with Chaoyangia. Zhou and Zhang (2006) later erected the taxa Chaoyangithiformes (credited to Hou, 1997) and Chaoyangornithidae (this time containing both Chaoyangia and Songlingornis). Both of these are malformed, as there is no "Chaoyangithes" or "Chaoyangornis". Moreover, both "Chaoyangidae" and "Chaoyangornithidae" are nomina nuda, as they were neither diagnosed nor defined (ICZN Article 13.1.1).
References- Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou, 228 pp.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Chaoyangia Hou and Zhang, 1993
C. beishanensis
Hou and Zhang, 1993
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype
- (IVPP V9934) (~235 mm) eleven dorsal vertebrae, eight dorsal ribs, dorsal rib fragments, three uncinate processes, gastralia(?), synsacrum, about five caudal vertebrae, ilia (one partial; 32 mm), pubes (51 mm), ischium (30 mm), femora (one incomplete; 45 mm), tibiotarsus, proximal fibula, tarsometatarsal fragment
Referred- ?(IVPP V9937) (Zhou and Hou, 2002)
Diagnosis- (after Hou, 1997) pneumatic foramen in femur(?).
(proposed) tapered preacetabular process; postacetabular process with subparallel dorsal and ventral edges anteriorly and a 75 degree angle posteriorly; obturator flange on ischium (also in Patagopteryx and Ornithurae sensu Chiappe).
Other diagnoses- Of the characters listed in the diagnosis by Hou and Zhang (1993), most are symplesiomorphies (non-heterocoelous dorsal vertebrae; uncinate processes; unfused pelvis; pelvis opisthopubic; preacetabular process longer than postacetabular process; pubic symphysis; femoral head well developed; fourth trochanter absent). The longitudinally grooved dorsal ribs are also present in Archaeorhynchus, Yanornis and Yixianornis, so are more widely distributed. Clarke (2002) notes there seven to eight sacral vertebrae, not more than eight as in Hou and Zhang's diagnosis. The supposedly unfused sacral centra may be ontogenetic. The ilium is described as "nephroid" and the femoral shaft "well developed", which are too vague to elaborate. The postacetabular process was described as expanded, but Hou and Zhang included portions of the sacrum in the postacetabular process (Zhou and Hou, 2002). The postacetabular process is actually tapered as in most maniraptorans. The pubis is reported to be pneumatized, which is otherwise only reported in Archaeopteryx among Mesozoic theropods, but difficult to determine in most specimens and of uncertain validity in Chaoyangia (perhaps the pubic shaft is hollow but non-pneumatic). The cnemial crest is equally well developed in Yixianornis and Yanornis.
Hou (1997) adds a few supposedly diagnostic characters. The thin-walled long bones (femur and presumably tibia) and fibula unfused to the tibia are symplesiomorphic for theropods. The femur is said to be pneumatized via a foramen on the proximolateral side, but this is only reported for Shixinggia among Mesozoic theropods. Hou's record of erroneous morphological interpretation makes me wary of accepting this character as valid.
Zhou and Hou (2002) add the character "uncinate processes long, slender and ventrally distributed to their diagnosis, but they are longer and more slender in Confuciusornis and similarly placed as well. They also state the postacetabular process is slightly rounded, but the posterior curvature is similar to Archaeorhynchus, though taller. A pubic symphysis of about a third of pubic length (30%) falls within the range of variation in Confuciusornis, and is not that different from Hongshanornis (26%) or Yanornis (35%). The trochanteric crest is equally high in taxa like Confuciusornis and Vorona. The rest of their new diagnostic characters are based on Songlingornis.
Comments- The holotype was discovered in 1990 and was merely referred to Aves order indet. by Hou and Zhang (1993). Other specimens were subsequently referred by Hou et al. (1996), but were later found to be from an indeterminate taxon closer to Aves than enantiornithines (IVPP V9937) or made the holotype of a new genus (IVPP V10913- Songlingornis). Hou (1997) states there are three cervicals and seven dorsals preserved, but such a low number of dorsals would be unheard of in a non-avian theropod, and it is more likely all ten presacral vertebrae are dorsals.
Chaoyangia a basal ornithuromorph? Hou et al. (1996) referred Chaoyangia to basal Euornithes sensu Sereno (their Ornithurae) due to the uncinate processes (now known to be present in many maniraptorans) and several characters preserved only in IVPP V10913.
Hou (1997) followed Hou et al.'s phylogenetic scheme, with additional evidence for Chaoyangia being a euornithine being ossified, pneumatized and elongated gastralia and a well developed cnemial crest. The gastralial characters are confusing, since no other euornithines known at the time preserved gastralia besides perhaps a couple elements in the probably incorrectly referred Liaoningornis. In any case, gastralia are symplesiomorphic for theropods, and are more elongate in basal taxa like Changchengornis (39% of femoral length) than in ornithuromorphs like Yixianornis (18%). Chaoyangia's are intermediate (28%). The only theropod with verified pneumatic gastralia is Aerosteon, and I am doubtful it can be verified in Chaoyangia, especially given Hou's history of misinterpretation and his additional claims of pneumaticity in the taxon (femur, pubis, etc.). The cnemial crest is as anteriorly elevated and pointed in some enantiornithines like Eoenantiornis and has yet to be analyzed on a broad scale in bird phylogeny.
Zhou (1999) found Chaoyangia to be a basal euornithine sensu Sereno (his Ornithurae) in his thesis. Additional characters not based on Songlingornis include- proximodorsal ischial process absent; ischium expanded distally due to low mid dorsal process (not present in Apsaravis, but seems valid); tall trochanteric crest (miscoded as absent in Confuciusornis and enantiornithines).
Zhang and Zhou (2000) included Chaoyangia in a version of Chiappe's bird matrix, finding it to be a basal euornithine sensu Sereno. In addition to the uncinate processes and characters based on Songlingornis, this was also due to the supposedly subparallel pelvic elements (miscoded as present in Chaoyangia), compressed pubic shaft (miscoded as present in Chaoyangia- Clarke, 2002), trochanteric crest (miscoded as absent in Confuciusornis, Protopteryx and Sinornis), and anterior cnemial crest (somewhat questionable, as it was coded unknown by Clarke).
Thus despite several miscodings and problematic characters, two characters support placing Chaoyangia closer to Passer than to Enantiornis- proximodorsal ischial process absent; ischium expanded distally due to low mid dorsal process.
Chaoyangia a basal pygostylian? Clarke (2002) is one of the few Western authors to comment on Chaoyangia. She found it to fall out as a pygostylian outside Ornithuromorpha. This was based on four characters which are more primitive than Patagopteryx + Aves. Yet more recent discoveries have shown some basal euornithines sensu Sereno are equally primitive in these characters- Archaeorhynchus has seven sacral vertebrae and an incompletely fused pelvis; Archaeorhynchus, Hongshanornis, songlingornithids and Gansus have pubic symphyses; and Archaeorhynchus, songlingornithids and Gansus have pubic boots. Clarke further noted that Chaoyangia was identical to Confuciusornis in all scored characters, and may be synonymous, but Confuciusornis differs in lacking a pubic boot, having a narrower postacetabular process, and a shorter ischium with a proximodorsal process and no mid dorsal process.
In conclusion, Chaoyangia seems to occupy a position closer to Passer than Enantiornis (Zhang and Zhou, 2000), but outside of Ornithuromorpha (Clarke, 2002).
Chaoyangia actually seems most similar to Archaeorhynchus, differing in that the postacetabular process is taller compared to its length with subparallel dorsal and ventral edges, the preacetabular process tapers anteriorly, the pubic peduncle is directed more posteriorly, the ischium is bowed dorsally, and the tibiotarsus is longer compared to the femur (>117%). It differs from Yixianornis (which is most closely related to Songlingornis) in having less sacral vertebrae, longer gastralia, an anteriorly tapered preacetabular process, no slender posteroventral postacetabular process, a pubic boot, and a longer ischium which is expanded distally.
Songlingornis- Hou et al. (1996) referred at least one additional specimen to Chaoyangia (IVPP V10913), which was later made the holotype of the new genus Songlingornis (Hou, 1997). The reference of IVPP V10913 to Chaoyangia was followed by Hou and Zhou (1999) and Zhou and Hou (2002), though the latter did indicate it had also been used as the holotype of Songlingornis. The specimens preserve few elements in common (though not none, as claimed by Clarke and Norell, 2001)- several dorsal vertebrae, dorsal ribs and proximal femur. The dorsals are alike in being non-heterocoelous, but this is similar to all non-hesperornithine, non-avian birds. Both femora are described as having proximally projecting trochanteric crests, shallow trochanteric fossae and large heads. These features are comparable to many basal birds including Confuciusornis and Vorona. The only point of difference in their descriptions in that Chaoyangia is said to have a "basically absent" neck, while Songlingornis has a "relatively well developed neck." Yet Chaoyangia's proximal femur has a near identical shape to Patagopteryx's, which has a neck, and Songlingornis' illustration is too schematic for proper comparison. Thus the taxa cannot be distinguished, but also share no synapomorphies that would allow them to be synonymized. Zhou and Hou (2002) referred a third specimen to Chaoyangia (IVPP V9937), but no further information is known, so it may be referrable to Songlingornis or another taxon instead.
References- Hou and Zhang, 1993. A new fossil bird from Lower Cretaceous of Liaoning: Vertebrata PalAsiatica. 31, 217-224.
Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: evidence from fossils from northeastern China. Science. 274, 1164-1167.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou, 228 pp.
Hou and Zhou, 1999. Paleornithology of China: A general review. Chinese Science Bulletin. 44(23), 2113-2116.
Zhou, 1999. Early evolution of birds and avian flight-evidence from Mesozoic fossils and modern birds. PhD Dissertation, Department of Systematics and Ecology, University of Kansas. 216 pp.
Zhang and Zhou, 2000. A primitive enantiornithine bird and the origin of feathers. Science. 290, 1955-1959.
Clarke and Norell, 2001. Fossils and avian evolution. Nature. 414, 508.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Zhou and Hou, 2002. The Discovery and Study of Mesozoic Birds in China. in Chiappe and Witmer, (eds.). Mesozoic Birds- Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 160-183.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
O'Connor and Zhou, 2013. A redescription of Chaoyangia beishanensis (Aves) and a comprehensive phylogeny of Mesozoic birds. Journal of Systematic Palaeontology. 11(7), 889-906.

Ornithuromorpha Chiappe et al., 1999
Definition- (Patagopteryx deferrariisi + Passer domesticus) (modified from Chiappe, 2002)
Other definitions- (Vorona berivotrensis + Patagopteryx deferrariisi + Passer domesticus) (modified from Chiappe, 2001)
= Ornithurae sensu Gauthier and de Queiroz, 2001
Definition- (tail shorter than the femur and with an upturned and ploughshare-shaped compressed pygostyle in the adult, composed of less than six segments, and shorter than the less than eight free caudals homologous with Vultur gryphus)
= Hongshanornithidae O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009
Definition- (Hongshanornis longicresta + Longicrusavis houi) (O'Connor, Gao and Chiappe, 2010)
Diagnosis- (proposed) peg and socket quadrate-quadratojugal articulation; quadrate pneumatic (absent in Hesperornithes); eleven or less dorsal vertebrae (unknown in Archaeorhynchus and Chaoyangia); nine or more sacral vertebrae; less than twelve caudal vertebrae (unknown in Archaeorhynchus and Chaoyangia); pygostyle less than four vertebrae in length; scapula longer than humerus (absent in Jianchangornis, Yanornis, Gansus and Hesperornis regalis); carpometacarpus fused distally; metacarpal I distal articulation shelf-like; pelvis completely fused; posterior trochanter absent on femur (unknown in Archaeorhynchus and Chaoyangia); distal vascular foramen enclosed by fusion of metatarsals III and IV (absent in basal Hesperornithes); hypotarsus present (unknown in Archaeorhynchus and Chaoyangia); at least one proximal vascular foramen in tarsometatarsus; metatarsal II ginglymoid (absent in Yanornis, some hesperornithines and Apsaravis).
Comments- O'Connor et al. (2009) propose Hongshanornithidae to include Hongshanornis and the at-the-time undescribed Longicrusavis. This is based on- dorsal dentary convex and dorsal surangular concave (also in Archaeorhynchus, many enantiornithines and probably Patagopteryx); posterolateral sternal processes not expanded much distally (probably symplesiomorphic as it is found in Archaeorhynchus, Gansus and basal enantiornithines); manus longer than humerus (probably symplesiomorphic as it is found in non-ornithothoracines, Protopteryx, Pengornis and Longipteryx); forelimb/hindlimb ratio (humerus+ulna / femur+tibia) <90% (also in Patagopteryx and hesperornithines). O'Connor et al. (2010) later described Longicrusavis and used the same matrix, also adding the manual formula of 2-3-2 to the diagnosis for Hongshanornithidae. Yet this is plesiomorphic, also being found in basal enantiornithines. Notably, Archaeorhynchus was not included in their matrix, Patagopteryx was coded as lacking the mandibular character even though the surangular is dorsally concave and the dentary missing, no enantiornithines with the mandibular character were included, Shanweiniao and Longipteryx were miscoded as having greatly expanded posterolateral sternal processes, and basal enantiornithines that have long manus and sternal processes with small expansions were not included. My preliminary analysis places Longicrusavis slightly closer to more derived birds than Hongshanornis.
References- O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.
O'Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.

Gargantuavis Buffetaut and Le Loeuff, 1998
G. philoinos Buffetaut and Le Loeuff, 1998
Late Campanian-Early Maastrichtian, Late Cretaceous
Marnes de la Maurine Formation, Aude, France
Holotype
- (MDE-CE-525) synsacrum (180 mm), partial ilia
Late Campanian-Early Maastrichtian, Late Cretaceous
Combebelle site, Herault, France
Paratype
- ?(MDE-A08) (141 kg) incomplete femur
Early Maastrichtian, Late Cretaceous
Fox Amphioux, Var, France
Referred
- ?(MDE coll.) synsacral fragment (Buffetaut et al., 1995)
Comments- Buffetaut et al. (1995) described a partial synsacrum of a large bird, which they left unnamed. Buffetaut and Le Loeuff (1998) later described two more specimens as a new taxon- Gargantuavis philoinos. They referred the femur because of its similar size and large trochanteric crest which could articulate with the holotype's antitrochanter, but this must be regarded as provisional. While they state the previously described synsacral fragment is similar to the middle of MDE-CE-525, they do not refer it explicitly to the taxon. They placed it as a non-ornithurine (sensu Chiappe) ornithuromorph, perhaps related to Patagopteryx.
References- Buffetaut, Le Loeuff, Mechin and Mechin-Salessy, 1995. A large French Cretaceous bird. Nature. 377, 110.
Buffetaut and Le Loeuff, 1998. A new giant ground bird from the Upper Cretaceous of southern France. Journal of the Geological Society, London. 155(1), 1-4.

"Zhyraornis" Nessov and Borkin, 1983
"Z. kashkarovi" Nessov and Borkin, 1983
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (TsNIGRI 43/11915) dorsal vertebra (6.9 mm)
Comments- This dorsal was originally included in a figure in Nessov and Borkin (1983), labeled as Zhyraornis kashkarovi. Yet that species was later described by Nessov (1984) based on a synsacrum (TsNIGRI 42/11915), with the dorsal vertebra as a paratype. As the name was not associated with a description in 1983, it is a nomen nudum and since it referred to a different specimen than what became Z. kashkarovi, it is given its own entry here. Nessov (1992) later regarded it as an indeterminate bird, while Kurochkin (1996) merely noted it was similar in size to Zhyraornis kashkarovi.
The dorsal is from an avebrevicaudan due to its large lateral central fossae, probably an ornithothoracine based on its age. It is not an enantiornithine, as the parapophyses are anteriorly placed, so may actually belong to Zhyraornis. It can also be excluded from Hesperornithes and Aves sensu stricto due to its amphicoely. It is here placed as Ornithuromorpha incertae sedis.
References- Nessov and Borkin, 1983. New records of bird bones from the Cretaceous of Mongolia and Soviet Middle Asia. USSR Academy of Sciences, Proceedings of the Zoological Institute. 116, 108-110 (in Russian).
Nessov, 1984. [Upper Cretaceous pterosaurs and birds from Central Asia] Paleontologicheskii Zhurnal. 1, 47-57.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.

unnamed ornithuromorph (Nessov, 1984)
Early Cenomanian, Late Cretaceous
Khodzhakul Formation, Uzbekistan
Material
- (TsNIGRI 57/11915) distal tarsometatarsus(?)
Comments- This was discovered in 1975 and briefly described and illustrated by Nessov (1984) as a possible distal tarsometatarsus of an aquatic bird. Nessov identified it as coming from the Beshtyuba Formation, but later (1992) determined that locality (Cholpyk or Tcelpyk) belongs to the Khodzhakul Formation instead. If it is indeed a fused distal tarsometatarsus, it is probably an ornithuromorph. Nessov notes metatarsal II ends more proximally than III and IV.
References- Nessov, 1984. [Upper Cretaceous pterosaurs and birds from Central Asia] Paleontologicheskii Zhurnal. 1, 47-57.
Nessov, 1992. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. in Campbell (ed). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.

unnamed ornithuromorph (Nessov, 1984)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan

Materal- (TsNIGRI 44/11915) proximal scapula
Comments- This scapula was originally a paratype of Zhyraornis kashkarovi (Nessov, 1984). Kurochkin (1996) later noted the acromion and glenoid showed "a certain similarity" to enantiornithines, but could not refer to to Zhyraornis itself (which he regarded as an enantiornithine). The elongate anteriorly projecting acromion and limited coracoid articulation indicates it is ornithothoracine, while Nessov noted the coracoid articular surface was weakly convex, unlike enantiornitines. Patagopteryx differs in having a transversely expanded acromion which is also ventrally constricted, distally flat and dorsally angled. That of Archaeorhynchus is smaller and more separated from the scapula ventrally. That of Yixianornis is slightly more slender and dorsally projected, and is separated ventrally from the bulbous coracoid tubercle. Ambiortus' acromion is different in being dorsoventrally compressed and having a dorsal tubercle, though the length and low coracoid tubercle are roughly similar. Apsaravis has a more elongate and hooked acromion, though the coracoid tubercle is similarly low. The scapulae of hesperornithines are highly reduced, while Ichthyornis has an apomorphically reduced acromion. Iaceornis' is narrower and hooked, with a bulbous coracoid tubercle. Those of Aves sensu stricto are generally dorsoventrally compressed. TsNIGRI 44/11915 is here referred to Ornithuromorpha incertae sedis, though it may belong to Zhyraornis.
References- Nessov, 1984. [Upper Cretaceous pterosaurs and birds from Central Asia] Paleontologicheskii Zhurnal. 1, 47-57.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.

unnamed ornithuromorph (Nessov, 1992)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan

Material- (PO 4605) proximal coracoid
Comments- Nessov (1992a) noted a coracoid with a "deep, round scapular facet", which seems to be the one later figured by him as possibly an ichthyornithiform (Nessov, 1992b). Note the specimen number is the same as a distal coracoid now referred to Abavornis species and labeled Aves in the same figure. Compared to Ichthyornis, it has a more proximolateral-distomedially oriented scapular cotyla, and a more laterally and less ventrally angled acrocoracoid which is dorsoventrally flatter. The concave scapular cotyla does indicate referral to Ornithuromorpha however.
References- Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. in Campbell (ed). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.

unnamed ornithuromorph (Nessov, 1992)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan

Material- (PO 3434b) distal tarsometatarsus
Comments- This specimen was listed as Aves indet. by Nessov (1992), but can be identified as an ornithuromorph by the high degree of distal fusion, including a distal vascular foramen. It is not hesperornithine, since metatarsal IV is less robust than III.
References- Nessov, 1992. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. in Campbell (ed). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.

unnamed probable ornithuromorph (Nessov, 1992)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan

Material- (PO 4607) dorsal vertebra (7 mm)
Comments- Nessov (1992a) noted an ichthyornithiform vertebra discovered in 1989, which seems to be a dorsal vertebra (PO 4607) later figured by him as Ichthyornis sp. (Nessov, 1992b). It is roughly similar to Ichthyornis, but the dorsals of that taxon are not diagnostic, and PO 4607 could come from another related taxon as well. It is from an avebrevicaudan due to its large lateral central fossae, probably an ornithothoracine based on its age. It is not an enantiornithine, as the parapophyses are anteriorly placed, and can be excluded from Hesperornithes and Aves sensu stricto due to its amphicoely.
References- Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. in Campbell (ed). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.

unnamed ornithuromorph (Dyke, Dortangs, Jagt, Mulder, Schulp and Chiappe, 2002)
Late Maastrichtian, Late Cretaceous
Maastricht Formation, Belgium
Material
- (NHMM/RD 271) jugals(?), quadrate(?) fragment, partial mandible, tooth, three dorsal vertebrae, distal scapula, proximal coracoid, incomplete humerus, distal ulna, proximal tarsal, proximal tarsometatarsus
Comments- Dyke et al. (2002) described this specimen as Ornithurae indet. (sensu Chiappe) based on the globular humeral head, and assigned it to Carinatae based on the prominent brachial fossa. However, the brachial fossa is also obvious in Longicrusavis and Gansus (though absent in Patagopteryx, Apsaravis and less importantly in Hesperornis). A globular humeral head is shared with all ornithuromorphs except patagopterygids. Thus the specimen is more derived than Patagopteryx, but not necessarily an ornithurine sensu Chiappe or a carinate. Clarke (2004) considered it Avialae incertae sedis because free proximal tarsals are generally absent in adult ornithuromorphs, but the specimen may not be adult and some subadult ornithuromorphs (e.g. Archaeorhynchus) are known to retain unfused astragali.
References- Dyke, Chiappe, Dortangs, Jagt and Schulp, 2002. A new ornithurine bird from the Maastricht Formation of Belgium; Was there a bottleneck in avian diversity at the end of the Cretaceous? Journal of Vertebrate Paleontology. 22(3), 50A.
Dyke, Dortangs, Jagt, Mulder, Schulp and Chiappe, 2002. Europe’s last Mesozoic bird. Naturwissenshaften. 89, 408-411.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.

undescribed possible ornithuromorph (Close and Vickers-Rich, 2009)
Aptian, Early Cretaceous
Wonthaggi Formation of the Strzelecki Group, Victoria, Australia
Material
- cervical vertebra
Comments- This was mentioned as a tentative ornithuromorph and described as small and heterocoelous.
Reference- Close and Vickers-Rich, 2009. Australia's Mesozoic birds: New material from the Early Cretaceous of Victoria. Journal of Vertebrate Paleontology. 29(3), 80A.

undescribed ornithuromorph (Galton, Dyke and Kurochkin, 2009)
Late Albian, Early Cretaceous
Cambridge Greensand, England

Material- (Booth Museum coll?) humerus
Comments- Galton et al. (2009) note an ornithurine humerus from the Cambridge Greensand, though which definition of Ornithurae they use is uncertain. This may be one of the seven bird elements from the Booth Museum (mentioned as "Enaliornis and Aves incertae sedis, including ends of humeri") to be described by Galton (in prep.).
References- Galton, Dyke and Kurochkin, 2009. Re-analysis of Lower Cretaceous fossil birds from the UK reveals an unexpected diversity. Journal of Vertebrate Paleontology. 29(3), 102A.
Galton, in prep. Additional bird bones (Hesperornithiformes Enaliornis and Aves incertae sedis) from the Early Cretaceous of England. Revue Paleobiologie.

undescribed ornithuromorph (O'Connor and Forster, 2009)
Maastrichtian, Late Cretaceous
Maevarano Formation, Madagascar

Material- synsacrum
Comments- O'Connor and Forster (2009) noted this as "referrable to Ornithurae" and state it exhibits distinct, transversely-oriented lumbosacral canals.
Reference- O'Connor and Forster, 2009. The Late Cretaceous (Maastrichtian) avifauna from the Maevarano Formation, Northwestern Madagascar: Recent discoveries and new insights related to avian anatomical diversification. Journal of Vertebrate Paleontology. 29(3), 157A.

Hongshanornis Zhou and Zhang, 2005
H. longicresta Zhou and Zhang, 2005
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Inner Mongolia, China

Holotype- (IVPP V14533) skull, mandibles, hyoids, at least seven cervical vertebrae, dorsal vertebrae, dorsal ribs, uncinate processes(?), gastralia, sacrum, caudal vertebrae, pygostyle, scapulae, coracoid, furcula, sternum, humeri (26 mm), radii, ulnae (24 mm), radiale, ulnare(?), carpometacarpi (13 mm), phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, manual unguals II, phalanges III-1, phalanges III-2, ilia, pubes (24 mm), ischium, femora (22 mm), tibiotarsi (38 mm), fibula, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsus (22 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV, body feathers, remiges, retrices
Referred- (DNHM D2945/6) (42 g) skull (30.5 mm), mandible, hyoid, eight cervical vertebrae, nine dorsal vertebrae, dorsal ribs, four uncinate processes, synsacrum, scapulae, coracoids, furcula, incomplete sternum, six sternal ribs, humeri (24.6 mm), radii, ulna (24.5 mm), radiale, carpometacarpus (13 mm), phalanx I-1, manual ungual I, phalanx II-1, phalanx II-2, manual ungual II, phalanx III-1, phalanx III-2, manual claw sheaths, partial ilia, distal pubes, femora (22 mm), tibiotarsi (35.5 mm), fibulae, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi (20.6 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, remiges, retrices, gastroliths (O'Connor et al., 2010)
(STM 35-3) skull, mandibles, seven cervical vertebrae, six dorsal vertebrae, dorsal ribs, synsacrum, partial scapula, coracoid, furcula, partial sternum, sternal ribs, incomplete humeri, radii, ulnae, radiale, ulnares, carpometacarpi, phalanges I-1, manual ungual I, phalanx II-1, phalanx III-1, partial ilia, pubis, femora, tibiotarsi, fibulae, seeds in crop, gastralia (Zhang et al., 2011)
over 24 specimens (Zheng et al., 2011)
Diagnosis- (from Zhou and Zhang, 2005) dentary ventrally curved (also in Archaeorhynchus); posterolateral sternal processes angled medially; hypocleidium present; forelimb/hindlimb (humerus+ulna / femur+tibiotarsus) ratio 83-85%.
Other diagnoses- Zhou and Zhang (2005) included additional characters in their diagnosis. A premaxilla with a slender and pointed anterior end is also present in Archaeorhynchus, Longicrusavis, songlingornithids and hesperornithines. Though they state both the premaxilla and maxilla are toothless, O'Connor et al. (2010) note alveoli are present in both. Similarly, contra Zhou and Zhang, Chiappe et al. (2014) find teeth in the dentary. A sternum with two pairs of posterior excavations is primitive for ornithothoracines. Chiappe et al. note the supposed tapering posterolateral process on the holotype's sternum is too poorly preserved to verify, and DNHM D2945/6 has either an expanded process or a fenestra. STM 35-3 shows expanded ends. A U-shaped furcula and laterally expanded manual phalanx II-1 are primitive for ornithuromorphs. Manual phalanx II-2 is also sinuously curved in Longicrusavis, Yixianornis and Gansus.
Miscoded originally? You et al. (2006) changed numerous codings for Hongshanornis based on personal observation from Chiappe and O'Connor. These include making the following states uncertain- dentary teeth absent (untrue- Chiappe et al., 2014); amount of upper beak formed by premaxilla (yet the suture seems clear and DNHM D2945/6 also has a short ventral margin); length of dorsal premaxilla process (yet the tip of the process is clearly seen); length of dorsal maxilla process; anterior extent of splenial; amphicoely of cervical centra; length/width ratio of dorsal centra (DNHM D2945/6 shows they were elongate); presence of uncinate processes (present in DNHM D2945/6); number of free caudal vertebrae (yet the pygostyle's position indicates it must be small); epicleidial morphology (hidden by matrix- Nesbitt et al., 2009); presence of procoracoid process; presence of lateral coracoid process (it seems absent in the photo of the holotype, but is definitely present in DNHM D2945/6); length of acromion process (long in DNHM D2945/6); depth of sternal keel; orientation of deltopectoral crest (yet it seems obviously dorsally projected in the photo and in DNHM D2945/6); prominence of bicipital crest; development of semilunate dorsal condyle on ulna (present in DNHM D2945/6); presence of ulnare (present in STM 35-3); fusion of carpometacarpus (completely fused in DNHM D2945/6 and seemingly in STM 35-3); convexity of medial edge of metacarpal I (it seems convex in the photo, but is definitely concave in DNHM D2945/6 and seemingly in STM 35-3); ginglymoidy of metacarpal I (seems flat in DNHM D2945/6); dorsal contact of ilia (at least unfused to sacral neural spines in DNHM D2945/6); orientation of postacetabular process; pubic orientation (the pubis is in anterior view, though O'Connor et al. state they are retroverted; definitely retroverted in DNHM D2945/6 and preserved to point posteriorly in STM 35-3); cross sectional shape of pubis (transversely compressed in DNHM D2945/6); presence of ilioischiadic fenestra; presence of proximodorsal ischial process (though O'Connor et al. state one is absent); presence of obturator flange; tibiotarsal fusion (astragalocalcaneum fused to tibia but with visible suture posteriorly in DNHM D2945/6); comparative width of tibiotarsal condyles (lateral largest in DNHM D2945/6); tarsometatarsal fusion (yet it seems present in the photo and is complete in DNHM D2945/6); absence of metatarsal V (yet the holotype and DNHM D2945/6 are complete enough to make its absence probably not taphonomic); ginglymoidy of metatarsal II (present in DNHM D2945/6). Additionally, they added several codings- dentary symphysis dorsally concave; dorsal centra with deep lateral fossae (as in DNHM D2945/6); gastralia present (as noted by Zhou and Zhang); lateral coracoid margin not convex (as in DNHM D2945/6 and STM 35-3; Chiappe et al. suggest the holotype is too poorly preserved to code); scapula subequal or longer than humerus (shorter in DNHM D2945/6); intermetacarpal process absent or present as a scar (process present in DNHM D2945/6); pubic boot absent (as noted by Zhou and Zhang, though DNHM D2945/6 has a pubic boot). Unfortunately, the photo of the specimen is small and often makes independant confirmation of states impossible.
References- Zhou and Zhang, 2005. Discovery of an ornithurine bird and its implication for Early Cretaceous avian radiation. Proceedings of the National Academy of Sciences. 102(52), 18998-19002.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Nesbitt, Turner, Spaulding, Conrad and Norell, 2009. The theropod furcula. Journal of Morphology. 270, 856-879.
O’Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.
Li, Zhou and Clarke, 2011. A reevaluation of the relationships among basal ornithurine birds from China and new information on the anatomy of Hongshanornis longicresta. 71st annual meeting, Society of Vertebrate Paleontology, Supplement to the online Journal of Vertebrate Paleontology. 144.
Zheng, Martin, Zhou, Burnham, Zhang and Miao, 2011. Fossil evidence of avian crops from the Early Cretaceous of China. Proceedings of the National Academy of Sciences of the United States of America. 108, 15904-15907.
Chiappe, Zhao, O'Connor, Gao, Wang, Habib, Marugan-Lobon, Meng and Cheng, 2014. A new specimen of the Early Cretaceous bird Hongshanornis longicresta: Insights into the aerodynamics and diet of a basal ornithuromorph. PeerJ. 2,e234.

Jianchangornis Zhou, Zhang and Li, 2009b
= "Jianchangornis" Zhou, Zhang and Li, 2009a
J. microdonta Zhou, Zhang and Li, 2009b
= "Jianchangornis microdonta" Zhou, Zhang and Li, 2009a
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China

Holotype- (IVPP V16708) (subadult) incomplete skull (72 mm), nine sclerotic plates, mandibles (one partial), hyoid, eight cervical vertebrae, seven dorsal vertebrae, eleven dorsal ribs, four gastralia, synsacrum (34 mm), pygostyle (5.5 mm), scapulae (53, ~47mm), coracoids (~30, 32 mm), furcula, sternum, humeri (75, 76 mm), radii (81, 78 mm), ulnae (82, 83 mm), radiale, ulnare, semilunate carpals, metacarpals I (10, 10 mm), phalanges I-1 (~25, 29 mm), manual unguals I (~9, ~9 mm), metacarpals II+III (mcII 34, 33 mm, mcIII ~32, 36 mm), phalanges II-1 (~20, ~18 mm), phalanges II-2 (~16, ~16 mm), manual unguals II (~4.5, ~6 mm), manual ungual III (~5.5 mm), ilia (38 mm), pubes (~51 mm), femora (59, 60 mm), tibiotarsi (75, 76 mm), fibulae (one proximal; 26 mm), pedal ungual I (~5.5 mm), tarsometatarsi (one incomplete; ~35, 37 mm), phalanx II-1 (12 mm), phalanges II-2 (11 mm), pedal unguals II (~6 mm), phalanges III-1 (15 mm), phalanges III-2 (11 mm), phalanges III-3 (10 mm), pedal ungual III (~7 mm), phalanx IV-1, phalanges IV-2 (8 mm), phalanges IV-3 (6 mm), phalanges IV-4 (7 mm), pedal ungual IV (~6 mm), feathers, fish fragments
Diagnosis- (after Zhou et al., 2009) at least 16 small, conical dentary teeth; strongly curved scapula; robust U-shaped furcula; robust and wide metacarpal I; manual digit I extends beyond metacarpal II; humerus+ulna+carpometacarpus / femur+tibiotarsus+tarsometatarsus ratio ~1.1.
Comments- This specimen was briefly described in an abstract (Zhou et al., 2009a) before being named and fully described later that year (Zhou et al., 2009b), though the former use is a nomen nudum due to ICZN Article 9.9. Including it in a version of Clarke's analysis, the authors found a basal euornithine polytomy consisting of Vorona, Archaeorhynchus, Jianchangornis, Hongshanornis, Patagopteryx, songlingornithids and more derived birds. Preliminary comparison suggests it is more derived than Archaeorhynchus based on having more than eight sacrals, a short pygostyle and distally fused metacarpals II and III, but less derived than Gansus and other birds based on having gastralia. The subequally wide tibiotarsal condyles may indicate is it more basal than Longicrusavis as well.
References- Zhou, Zhang and Li, 2009a. A new basal ornithurine bird from the Lower Cretaceous of China. Journal of Vertebrate Paleontology. 29(3), 207A.
Zhou, Zhang and Li, 2009b. A new basal ornithurine bird (Jianchangornis microdonta gen. et sp. nov.) from the Lower Cretaceous of China. Vertebrata PalAsiatica. 47(4), 299-310.

Piscivoravis Zhou, Zhou and O'Connor, 2013
P. lii Zhou, Zhou and O'Connor, 2013
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China

Holotype- (IVPP V17078) (subadult) posterior skull, posterior mandible, partial hyoids, ten cervical vertebrae, twelve dorsal vertebrae, thirteen dorsal ribs (some partial), uncinate processes, several gastralia, synsacrum, three caudal vertebrae, pygostyle, scapula (61 mm), coracoid (35 mm), incomplete furcula, sternum, humerus (74 mm), radius (75 mm), ulna (77 mm), radiale, ulnare, carpometacarpus (mcI 7, mcII 34, mcIII 34 mm), phalanx I-1 (17 mm), manual ungual I (10 mm), phalanx II-1 (15 mm), phalanx II-2 (15 mm), manual ungual II (6 mm), phalanx III-1 (9 mm), ilia, pubes (~63 mm), ischia, femora (56 mm), tibiotarsi (71 mm), fibulae (one incomplete; 33 mm), metatarsals I (6 mm), phalanges I-1 98 mm), pedal unguals I (5 mm), tarsometatarsi (35 mm), phalanges II-1 (12 mm), phalanges II-2 (11 mm), pedal unguals II (7 mm), phalanges III-1 (13 mm), phalanges III-2 (one partial; 10 mm), phalanx III-3 (10 mm), pedal ungual III (7 mm), phalanges IV-1 (10 mm), phalanges IV-2 (8 mm), phalanges IV-3 (6 mm), phalanx IV-4 (7 mm), pedal ungual IV (6 mm), body feathers, remiges, retrices, fish bones
Diagnosis- (after Zhou et al., 2013) anterior 1/3-1/2 of pubis dorsomedially excavated by deep groove; synsacrum with tall spinous crest that diminishes posteriorly; furcula with strongly tapered omal tips; sternum broad, width greater than length; scapula long, tapered and distally constricted; deltopectoral crest anteriorly deflected; large and strongly curved manual unguals; (humerus+ulna+mcII)/(femur+tibiotarsus+mtIII) ~ 1.14; two well-developed cnemial crests on tibiotarsus.
Comments- Zhou et al. (2013) added Piscivoravis to a version of Clarke's analysis and found it to be a basal ornithoromorph in a polytomy with Patagopteryx, Jianchangornis and more derived taxa.
Reference- Zhou, Zhou and O'Connor, 2013. A new piscivorous ornithuromorph from the Jehol Biota. Historical Biology. http://dx.doi.org/10.1080/08912963.2013.819504

Schizooura Zhou, Zhou and O'Connor, 2012
S. lii Zhou, Zhou and O'Connor, 2012
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China

Holotype- (IVPP V16861) skull (52 mm), mandibles, eleven cervical vertebrae, posterior six dorsal vertebrae, partial dorsal ribs fused to uncinate process, gastralia, synsacrum, eight caudal vertebrae, pygostyle (20 mm), scapulae (one partial; 50 mm), coracoids (29 mm), furcula, sternum, sternal ribs, humeri (60 mm), radii (57 mm), ulnae (64 mm), radiales, ulnares, metacarpals I (6 mm), phalanges I-1 (one partial; 12 mm), manual unguals I (3.5 mm), carpometacarpi (30 mm; mcII 22, mcIII 23 mm), phalanges II-1 (one incomplete; 14 mm), phalanges II-2 (14 mm), manual unguals II (3.5 mm), phalanx III-1 (5 mm), ilia (one incomplete, one partial), incomplete pubes (~45 mm), ischium, femora (~45 mm), tibiotarsi (62 mm), partial fibula, metatarsals I, phalanges I-1 (5 mm), pedal unguals I (4 mm), tarsometatarsi (36 mm), phalanges II-1 (10 mm), phalanges II-2 (7 mm), pedal unguals II (5 mm), phalanges III-1 (10 mm), phalanges III-2 (7 mm), phalanges III-3 (6 mm), pedal unguals III (6 mm), phalanx IV-1 (~9 mm), phalanges IV-2 (6 mm), phalanges IV-3 (4 mm), phalanges IV-4 (4 mm), pedal unguals IV (5 mm), body feathers, remiges, retrices
Diagnosis- (after Zhou et al., 2012) toothless; dorsal premaxilla process contacts frontals; jugal slender; robust, V-shaped furcula with short hypocleidium; robust humerus with large deltopectoral crest that extends ~50% of humeral length; (humerus+ulna+mcII)/(femur+tibiotarsus+tarsometatarsus) ratio ~1.01; tarsometatarsotibiotarsal ratio high (0.58).
Reference- Zhou, Zhou and O'Connor, 2012. A new basal beaked ornithurine bird from the Lower Cretaceous of Western Liaoning, China. Vertebrata PalAsiatica. 50(1), 9-24.

Yumenornis Wang, O'Connor, Li and You, 2013
Y. huangi Wang, O'Connor, Li and You, 2013
Early Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype
- (GSGM-06-CM-013) scapula, coracoid, partial furcula, partial sternum, sternal ribs, humerus (49.9 mm), radius (49.7 mm), ulna (52.9 mm), ulnare, carpometacarpus (27 mm), phalanx I-1 (10.9 mm), manual ungual I (5.4 mm), phalanx II-1 (12.1 mm), phalanx II-2 (11.5 mm), manual ungual II (4.2 mm), phalanx III-1 (6.7 mm)
Diagnosis- (after Wang et al., 2013) sternum with angular rostral margin (~90°), lateral (zyphoid) processes, and robust, distally expanded lateral trabeculae; radius with deep distal fossa; ratio of length of manus relative to humerus 1.1.
Comments- Wang et al. (2013b) entered this into O'Connor's matrix and found it to be a basal ornithomorph in large polytomy with taxa less derived than Ichthyornis but more derived than Patagopteryx.
References- Wang, O'Connor, Li and You, 2013a. A new ornithuromorph bird from the Early Cretaceous Changma Basin of Gansu Province, Northwestern China. Journal of Vertebrate Paleontology. Program and Abstracts 2013, 234-235.
Wang, O'Connor, Li and You, 2013b. Previously unrecognized ornithuromorph bird diversity in the Early Cretaceous Changma Basin, Gansu Province, Northwestern China. PLoS ONE. 8(10), e77693.

Patagopterygiformes Alvarenga and Bonaparte, 1992
Definition- (Patagopteryx deferrariisi <- Passer domesticus) (Martyniuk, 2012)
= Patagopterygidae Alvarenga and Bonaparte, 1992
Diagnosis- humeral head not domed proximally; anteriorly projected deltopectoral crest (also in Longicrusavis and Aves); shallow capital groove on humerus (also in Apsaravis and Ambiortus).
References- Alvarenga and Bonaparte, 1992. A new flightless landbird from the Cretaceous of Patagonia. Los Angeles County Museum of Natural History, Science Series. 36, 51-64.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Patagopteryx Alvarenga and Bonaparte, 1992
P. deferrariisi Alvarenga and Bonaparte, 1992
Santonian, Late Cretaceous
Bajo de la Carpa Formation of the Rio Colorado Subgroup, Neuquen, Argentina

Holotype- (MACN-N-03) (~545 mm) ninth cervical vertebra (17.5 mm), tenth cervical vertebra (16.5 mm), eleventh cervical vertebra (16 mm), twelfth cervical vertebra (14.8 mm), thirteenth cervical vertebra (13.2 mm), first dorsal vertebra (10.4 mm), second dorsal vertebra (10.3 mm), third dorsal vertebra (9.8 mm), fourth dorsal vertebra (10.5 mm), fifth dorsal vertebra (12 mm), sixth dorsal vertebra (11.5 mm), seventh dorsal vertebra (11.8 mm), eighth dorsal vertebra (12 mm), ninth dorsal vertebra (11.8 mm), tenth dorsal vertebra (9.4 mm), eleventh dorsal vertebra (10.1 mm), synsacrum (52.6 mm), two caudal vertebrae (9 mm), proximal scapulae, proximal coracoids, humeri (one incomplete; 66.3 mm), proximal radius, proximal ulna, ilia (one incomplete; 68.4 mm), femora (one partial; ~103 mm), incomplete tibiotarsus (~140 mm), partial tarsometatarsus, phalanx II-1, phalanx III-1, phalanx IV-1, phalanx IV-2, phalanx IV-3
Paratypes- (MACN-N-10) (at least three individuals) proximal tarsometatarsus, distal tarsometatarsus, three fragments of tarsometatarsi, pedal phalanges
(MACN-N-11) posterior skull, posterior mandibles, proatlas, atlas, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, four dorsal vertebrae, two dorsal ribs, five caudal vertebrae, scapula, incomplete coracoids (38 mm), partial sternum, incomplete humeri (59.8 mm), radius, incomplete ulnae (~52 mm), carpometacarpus (~23 mm), partial phalanx II-1, phalanx II-2, manual ungual II, partial ilia, pubes (one incomplete; ~50 mm), incomplete ischia (52.5 mm), femur (~100 mm), tibiotarsus (~137 mm), partial fibula, metatarsals I (14.8 mm), phalanges I-1, pedal unguals I, tarsometatarsi (50.8 mm), phalanges II-1, phalanges II-2, pedal ungual II, phalanges III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV
Referred- (MACN-N-14) second dorsal vertebra (11.6 mm), third dorsal vertebra, fourth dorsal vertebra, fifth dorsal vertebra (~12 mm), vertebral fragments (Chiappe, 1992)
(MUCPv-48) skull fragments including braincase, posterior dorsal vertebra, several vertebrae, mid caudal vertebra (10.3 mm), pelvic fragments including partial ilium, incomplete femur (~98 mm), incomplete tibiotarsus (~141 mm), fibula (~112 mm), phalanx I-1, pedal ungual I, tarsometatarsus (51 mm), phalanx II-1, phalanx II-2, proximal pedal ungual II, phalanx III-1, distal phalanx III-2, phalanx III-3, pedal ungual III, partial pedal ungual IV (Chiappe, 1991)
(MUCPv-207) several vertebrae, partial synsacrum, mid caudal vertebrae, partial hindlimb (Chiappe, 1992)
Diagnosis- (after Alvarenga and Bonaparte, 1992) cervical vertebrae completely heterocoelous (also in Ornithurae sensu Chiappe); dorsal vertebrae 6-11 procoelous; reduced forelimbs; large lateral process on distal postacetabular process; medial process on distal postacetabular process.
(after Chiappe, 1996a) quadrate fused to pterygoid; quadrate foramen present laterally; fifth dorsal vertebra biconvex; posterior dorsal vertebrae with very wide reniform centra; posterior articular surface of synsacrum convex; acromion transversely expanded anteriorly; proximal end of coracoid with dorsally projecting section for scapular articulation; two prominent intermuscular lines on dorsal shaft of humerus; distal ulna extremely anteroposteriorly compressed; metacarpal III more robust than metacarpal II; strong medial laminar process on metacarpal II (a reduced metacarpal I?); pubis anteroposteriorly compressed; distal pubis anteriorly curved; prominent m. iliofibularis tubercle on fibula; distal fibula fused to anterior side of tibiotarsus; minimum width of tarsometatarsus over 20% of length; untwisted metatarsal I.
(after Chiappe, 2002a) acromion dorsoventrally expanded at tip (also in Apsaravis).
(proposed) quadrate with posterior condyle distally (also in Aves); basipterygoid processes elongate; articular not pneumatic (also in Hesperornis regalis); dorsal centra lack lateral excavations (also in Carinatae); coracoid articulations on sternum widely separated (also in Hesperornis crassipes); deltopectoral crest reduced in height (also in derived hesperornithines and Aves); bicipital crest lacks fossae (also in Songlingornithidae and derived hesperornithines); brachial fossa absent on ulna (also in Archaeorhynchus); antitrochanter placed directly posterior to acetabulum; pubic symphysis absent (also in Carinatae sensu Chiappe); proximodorsal process on ischium; obturator flange on ischium (also in Chaoyangia and Ornithurae sensu Chiappe); pubic boot absent (also in Ornithurae sensu Chiappe); m. tibialis cranialis tubercle on metatarsus absent (also in Archaeorhynchus).
Other diagnoses- Some of Alvarenga and Bonaparte's (1992) diagnostic characters are symplesiomorphic- notarium absent; anterior articular surface of synsacrum strongly concave; synsacrum dorsoventrally compressed; synsacrum transversely wide; humerus lacks pneumotricipital foramen; ilium weakly fused to synsacrum; preacetabular process vertically oriented; preacetabular process laterally far from synsacrum; iliac crest single and extends to posterior margin of ilium; opisthopubic pelvis; ilioischial fenestra open; iliopubic fenestra open; lateral cnemial crest anteriorly developed; supratendinal bridge absent on tibiotarsus.
Of Chiappe's (2002a) diagnostic characters, the prominent iliac crest is plesiomorphic for avepods and the "well developed caudolateral spine" seems to be the supratrochanteric process common in basal birds. The ischium is also paddle-shaped in Yixianornis, Gansus, Ichthyornis and Iaceornis.
Comments- The holotype and MACN-N-10 were discovered in 1984, while MACN-N-11 was discovered in 1985. They were first commented on by Bonaparte (1986), who described them as ratite-like. Chiappe (1991) noted the description of the then unnamed taxon was in press, also mentioning MUCPv-48 as "housed in the UNC". The taxon was formally described by Alvarenga and Bonaparte (1992), and redescribed by Chiappe, first in his unpublished thesis (1992), then in 1996a, and finally in depth in 2002a. Chinsamy et al. (1994, 1995) described its histology.
Alvarenga and Bonaparte (1992) stated there are indications that the then unprepared MACN-N-11 lacked a pygostyle, but this cannot be confirmed. The supposed furcular epicleidia in the holotype were later determined to be proximal coracoids (Chiappe, 1996). The supposed distal coracoid preserved in the holotype is probably not a Patagopteryx element (Chiappe, 1996). Hutchinson (2001) identified a proximodorsal ischial process and an obturator flange.
Patagopteryx a palaeognath? Alvarenga and Bonaparte (1992) and Alvarenga (1993) proposed a close relationship to palaeognaths, rheiforms in particular, but also lithornithiforms, tinamiforms, casuariiforms and apterygiforms. Characters supporting this are largely symplesiomorphic for birds- elongate acromion on scapula; pneumotricipital foramen absent (a reversal in ratites); open ischiopubic fenestra; open ilioischiadic fenestra; deep and triangular popliteal fossa; robust and anteriorly developed lateral cnemial crest; supratendinal bridge absent (probably a reversal in some lithornithids and ratites); round lateral tibiotarsal condyle; reduced hypotarsus (a reversal in ratites). "General form and proportions" of cervical vertebrae being similar to tinamiforms is too vague to evaulate. The supposedly horizontal postacetabular process would be primitive for carinates, but seems to be untrue in Patagopteryx in any case. Patagopteryx's trochanteric crest is not wide and planar laterally, as it has a lateral ridge and ITCR insertion scar. The trochanteric crest does not appear more anteriorly exoanded than enantiornithines or Vorona. The supposedly medially placed tendinal groove is instead a depression formed by the extensor retinaculum ridges as in Apsaravis (Clarke and Norell, 2002), so is not homologous to the condition in palaeognaths. The tibiotarsal intercondylar groove is not particularly shallow or wide, contra Alvarenga and Bonaparte. Chiappe (1995) noted there is no "tendency for the ischia to become horizontal and approach each other medially", though the latter would be primitive for birds. Chiappe also notes Patagopteryx has a single cnemial crest, not two in which the "inner is formed over the outer" as is apparently the case in some ratites. The dorsoventrally flattened posterior dorsal centra and anteroposteriorly compressed ulna are apparently similar to rheiforms and are otherwise unknown in basal ornithuromorphs.
Kurochkin (1995) placed Patagopteryx within Ratitae based on several characters. The heterocoelous cervical vertebrae are symplesiomorphic for avians, and are found in some basal ornithuromorphs like Apsaravis and hesperornithines as well. The dorsals are said to be "transitional to heterocoely or procoelous", but Patagopteryx also has opisthocoelous and biconvex dorsals. Heterocoelous dorsals are similar to Aves and Hesperornithes, but no palaeognaths seem to have procoelous dorsals. Contra Kurochkin, the tibiotarsus lacks an anterior cnemial crest, which would be symplesiomorphic for a more inclusive clade than Ratitae in any case. The completely fused tarsometatarsus is symplesiomorphic for ornithuromorphs. A hallux with two phalanges is symplesiomorphic for all reptiles.
There are a few additional Aves characters which Patagopteryx does possess- a tricondylar quadrate articulation; the deltopectoral crest is oriented anteriorly (also in Alamitornis); the deltopectoral crest is lower than shaft width (also in Alamitornis and hesperornithines); pubic symphysis absent (also in Apsaravis, hesperornithines and Carinatae). While there are several characters shared with Aves and a couple apparently shared with Rheiformes, these are outweighed by the large number of characters suggesting a more basal position, as described below.
Patagopteryx a hesperornithine? Chatterjee (1999) performed a phylogenetic analysis which found Patagopteryx to be the sister taxon of Hesperornithiformes. This was only based on the ulna being shorter than the humerus (miscoded in Ichthyornis and now also known to be true in Hongshanornis and Apsaravis) and the supposedly absent distal trochlear surface on the ulna (actually unknown in Patagopteryx). In addition, Patagopteryx has to reverse the spherical head found in ornithurines sensu Chiappe in Chatterjee's cladogram. Thus there is basically no support for plaving Patagopteryx in Hesperornithes.
Patagopteryx an enantiornithine? Feduccia (1999) listed Patagopteryx under Enantiornithes, though he did not mention reasons besides noting both Patagopteryx and Lecho Formation enantiornithines have LAGS in their femoral histology. However, these are also present in Rahonavis, so are probably plesiomorphic. While Patagopteryx does share a few characters with enantiornithines (e.g. some of the latter have tarsometatarsi which are excavated posteriorly), it has many more euornithine characters.
Patagopteryx a basal ornithuromorph? Technically, Patagopteryx is by definition a basal ornithuromorph, but it is understood here as implying the genus is closer to Passer than to Enantiornis, but less derived than ichthyornithines, hesperornithines or Aves. Chiappe (1991) first suggested the then unnamed Patagopteryx was unrelated to any ornithurine (sensu Chiappe). His 1992 thesis proposed it was basal to his concept of Ornithurae, though this was not published until Chiappe and Calvo (1994) (elaborated on in Chiappe, 1995). That phylogenetic analysis supported excluding Patagopteryx from Ornithurae sensu Chiappe as the basalmost ornithuromorph based on- pterygoid process of quadrate rounded; more than ten dorsal vertebrae (now also known to be more primitive than songlingornithids, Apsaravis and Gansus); uncinate processes absent (probably untrue, as only a few ribs are preserved and uncinates are primitive for maniraptorans); procoracoid process absent (now also known to be more primitive than Archaeorhynchus, Hongshanornis, Ambiortus, songlingornithids and Gansus); humeral head anteriorly concave (now also known to also be more primitive than Hongshanornis, Ambiortus, songlingornithids, Apsaravis and Gansus); acetabulum >11% of ilial length (now also known to be more primitive than songlingornithids and Gansus); pubis and ischium not parallel to ilium (now also known to be more primitive than Apsaravis and Gansus); pubis not laterally compressed (now known also to be more primitive than Apsaravis); femur lacks patellar groove (now also known to be more primitive than Apsaravis and Gansus); anterior cnemial crest absent (now also known to be more primitive than Archaeorhynchus and Gansus); m. iliofibularis tubercle of fibula not posteriorly oriented (now also known to be more primitive than Gansus); metatarsal III not plantarily displaced proximally (now also known to be more primitive than songlingornithids, Apsaravis and Gansus); intercotylar eminence of tarsometatarsus poorly developed. In 1996a, Chiappe performed another analysis which added an additional character to support this- articular not pneumatic (now also known to be more primitive than Archaeorhynchus). In 2001 (repeated in 2002b), Chiappe expanded the analysis once more, finding Patagopteryx and Vorona to be basal to ornithurines sensu Chiappe. Added characters which supported excluding Patagopteryx from the latter clade are- anterior articular surface of synsacrum strongly concave (somewhat ambiguous, as it is somewhat concave in most coelurosaurs); extensor canal absent on tibiotarsus (now also known to be more primitive than Archaeorhynchus, songlingornithids and Apsaravis); wide medial condyle on tibiotarsus (now also known to be more primitive than Apsaravis and Gansus); transverse groove proximally undercuts tibiotarsal condyles (now also known to be more primitive than Gansus and probably Archaeorhynchus).
Norell and Clarke (2001) first published Clarke's matrix, which found Patagopteryx was not only basal to ornithurines sensu Chiappe, but also their new taxon Apsaravis. Additional basal ornithuromorphs have subsequently been added to the matrix (Hongshanornis, Archaeorhynchus, Ambiortus, songlingornithids, Gansus), which have all ended up more derived than Patagopteryx as well. New characters which support placing Patagopteryx outside Ornithurae sensu Chiappe are- less than ten sacral vertebrae (also more primitive than Apsaravis and Gansus); humerus not domed proximally (also more primitive than Archaeorhynchus, Hongshanornis, Ambiortus, songlingornithids, Apsaravis and Gansus); radius without muscle impression along ventroposterior surface (also more primitive than Archaeorhynchus and Apsaravis); metacarpal III >50% of width of metacarpal II (also more primitive than Yanornis, Yixianornis and Apsaravis); manual phalanx II-1 not strongly compressed dorsoventrally (also more primitive than Archaeorhynchus, Hongshanornis, Ambiortus, songlingornithids, Apsaravis and Gansus); antitrochanter directly posterior to acetabulum (probably a reversal, as more basal ornithurines sensu Gauthier have the opposite state); only one proximal vascular foramen on tarsometatarsus; fossa for metatarsal I on tarsometatarsus absent. In addition, Patagopteryx can be excluded from Carinatae due to- dorsal vertebrae lack ossified tendons on transverse processes; sacral vertebrae lack a series with short dorsally oriented transverse processes (also more primitive than Gansus). Finally, it can be excluded from Aves based on- quadrate foramen not located posteromedially; less than fifteen sacral vertebrae; no pneumatic foramen in humerus; the ilium does not overlap any dorsal ribs (also more primitive than Gansus); distal vascular foramen with one exit.
Cau and Arduini (2008) found Patagopteryx in a similar position, basal to all ornithuromorphs except Vorona. New characters influencing this position are- large hypapophyses absent in mid dorsals (also more primitive than Gansus); mid sacral centra not transversely compressed (also more primitive than Gansus); coracoid lateral process absent (this is miscoded in Patagopteryx); sternal keel absent (probably a reversal due to flightlessness, as Confuciusornis sometimes has a keel); manual phalanx II-2 longer than II-1 (also more primitive than Ambiortus, songlingornithids and Gansus); proximodorsal process on ischium (also more primitive than Archaeorhynchus, Chaoyangia, songlingornithids, Apsaravis and Gansus); fibula longer than half tibiotarsal length (also more primitive than Hongshanornis, songlingornithids and Gansus). Additionally, it is excluded from Carinatae based on- acrocoracoid process not hooked medially; coracoid foramen absent (miscoded in Aves, as it is absent in most, so not valid for excluding Patagopteryx); metatarsal II ginglymoid (miscoded in Ichthyornis and polymorphic in Aves, so not very useful for excluding Patagopteryx).
Gao et al. (2008) also found Patagopteryx to be an ornithuromorph basal to Aves and Gansus. O'Connor et al. (2009) later used the same matrix with other ornithuromorphs added (Hongshanornis, PKUP V1069, Apsaravis, Yanornis, Hesperornis, Ichthyornis) and found Patagopteryx to be basal to all of them. New characters supporting this include- well developed olecranon fossa absent in humerus (also absent in Apsaravis, Hesperornithes and Ichthyornis; so probably convergent in Yixianornis and Aves, but does exclude Patagopteryx from the latter); m. scapulotriceps groove absent in humerus (also absent in Apsaravis, some Ichthyornis and palaeognaths; so probably convergent in Yixianornis and Neognathae); ischium >66% of pubic length (highly homoplasic once taxa that aren't included by have long ischia like Apsaravis, Hesperornithes and Iaceornis are taken into account); metatarsal I not twisted. In addition, the ungual on manual digit II excludes it from Iaceornis+Aves and lack of hypotarsal grooves excludes it from Aves. Some other characters (e.g. open iliosacral canals) are listed as avian (their neornithine) synapomorphies but not considered here, as they are actually neognath characters which only appear as avian characters since no palaeognaths were included.
Thus there are about 29 valid characters excluding Patagopteryx from Ornithurae sensu Chiappe, three additional characters excluding it from Carinatae and six others exclude it from Aves.
References- Bonaparte, 1986. History of terrestrial Cretaceous vertebrates of Gondwana. Simposio Bioestratigrafía del Paleozoico Inferior: IV Congreso Argentino de Paleontología y Bioestratigrafía, Mendoza, Argentina. 2, 63-95.
Chiappe, 1989. Flightless birds from the Late Cretaceous of Patagonia. Archosaurian Articulations. 1(10), 73-77.
Chiappe, 1991. Cretaceous birds of Latin-America. Cretaceous Research. 12, 55-63.
Alvarenga and Bonaparte, 1992. A new flightless landbird from the Cretaceous of Patagonia. Los Angeles County Museum of Natural History, Science Series. 36, 51-64.
Chiappe, 1992. Osteologia y sistematica de Patagopteryx deferrariisi Alvarenga y Bonaparte (Aves) del Cretacico de Patagonia. Filogenia e historia biogeografica de las aves Cretacicas de America del Sur. PhD Thesis. Universidad de Buenos Aires.
Alvarenga, 1993. A origem das aves seus fosseis. in Andrade (ed). A Vida das Aves. pp. 16-26.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Upper Cretaceous bird (Enantiornithes: Avisauridae) from Patagonia, Argentina. Journal of VertebratePaleontology. 14(2), 230-246.
Chinsamy, Chiappe and Dodson, 1994. Growth rings in Mesozoic birds. Nature. 368, 196-197.
Chiappe, 1995. The phylogenetic position of the Cretaceous birds of Argentina: Enantiornithes and Patagopteryx deferrariisi. Courier Forschungsinstitut-Senckenberg. 181, 55-63.
Chinsamy, Chiappe and Dodson, 1995. Mesozoic avian bone microstructure: Physiological implications. Paleobiology. 21(4), 561-574.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Chiappe, 1996a. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Chiappe, 1996b. Early avian evolution in the southern hemisphere: Fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum. 39, 533-556.
Chatterjee, 1999. Protoavis and the early evolution of birds. Palaeontographica A. 254, 1-100.
Feduccia, 1999. The Origin and Evolution of Birds. Yale University Press, New Haven, CT. 466 pp.
Chiappe, 2001. Phylogenetic relationships among basal birds. In Gauthier and Gall (eds). New perspectives on the origin and early evolution of birds: Proceedings of the international symposium in honor of John H. Ostrom. New Haven: Peabody Museum of Natural History. 125-139.
Hutchinson, 2001. The evolution of pelvic osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnean Society. 131, 123-168.
Norell and Clarke, 2001. Fossil that fills a critical gap in avian evolution. Nature. 409, 181-184.
Chiappe, 2002a. Osteology of the flightless Patagopteryx deferrariisi from the Late Cretaceous of Patagonia (Argentina). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 281-316.
Chiappe, 2002b. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Clarke and Norell, 2002. The morphology and phylogenetic position of Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum Novitates. 3387, 46 pp.
Cau and Arduini, 2008. Enantiophoenix electrophyla gen. et sp. nov. (Aves, Enantiornithes) from the Upper Cretaceous (Cenomanian) of Lebanon and its phylogenetic relationships. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano. 149(2), 293-324.
Gao, Chiappe, Meng, O'Conner, Wang, Cheng and Liu, 2008. A new basal lineage of Early Cretaceous birds from China and its implications on the evolution of the avian tail. Palaeontology. 51(4), 775-791.
O'Conner, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.

Alamitornis Agnolin and Martinelli, 2009
= "Alamitornis" Agnolin and Martinelli, 2008 online
A. minutus Agnolin and Martinelli, 2009
= "Alamitornis minutus" Agnolin and Martinelli, 2008 online
Campanian-Maastrichtian, Late Cretaceous
Los Alamitos Formation, Rio Negro, Argentina

Holotype- (MACN PV RN 1108) proximal humerus
Paratype- (MACN PV RN 1109) five proximal humeri
Referred- ?(MACN PV RN 1110) (juvenile) distal femur
Diagnosis- (after Agnolin and Martinelli, 2008) deltopectoral crest proximodistally short and subtriangular; medial tuber placed distally compared to humeral head.
Other diagnoses- Agnolin and Martinelli (2008) originally included "humeral shaft very thin mediolateraly distal to proximal end" in their diagnosis, but while the shaft is narrower compared to the proximal end (37% of the width across the medial tubercle and humeral head) compared to Patagopteryx (~47%), several other basal ornithuromorphs have similarly narrow shafts (Archaeorhynchus 34%, Hongshanornis ~38%, Ichthyornis 37%).
Comments- The paper describing Alamitornis was originally available online in September 2008, though the identical paper version which the ICZN recognizes was not published until February 2009.
Agnolin and Martinelli proposed several similarities to Patagopteryx. The lack of a pneumatic foramen only excludes it fron Aves. The anteriorly directed deltopectoral crest is similar to both Patagopteryx and Aves. The sigmoid proximal outline of the humerus is due to this and the plesiomorphically concave anterior edge. The proximally globular humeral head is similar to most non-enantiornithine birds, including basal taxa like Confuciusornis and derived ones like Ichthyornis. The capital groove is not narrower in patagopterygids than other ornithuromorphs like Yixianornis and Ichthyornis, but may be shallower (though Apsaravis and Ambiortus have shallow grooves as well, since they lack them entirely). The well excavated proximal anterior surface of the humerus is similar to enantiornithines and Apsaravis in addition to Patagopteryx. The medial tuber does not protrude more than other ornithuromorphs. Contra Agnolin and Martinelli, Patagopteryx seems to lack much of a lateral supracondylar ridge on its femur, though this is seen in some enantiornithines (e.g. Vorona, Concornis, Neuquenornis). A strong m. iliofibularis tubercle on the distal femur is found in Patagopteryx, but also some enantiornithines (e.g. Vorona, PVL-4037). Agnolin and Martinelli provisionally assign Alamitornis to Patagopterygiformes due to these characters, and I agree it may be related to Patagopteryx based on the anteriorly directed deltopectoral crest and shallow capital groove.
Reference- Agnolin and Martinelli, 2009. Fossil birds from the Late Cretaceous Los Alamitos Formation, Río Negro province, Argentina. Journal of South American Earth Sciences. 27, 42-49.

unnamed clade (Longicrusavis houi + Passer domesticus)
Diagnosis- (proposed) bicipital crest strongly projected (absent in Aves); brachial fossa on humerus well developed (absent in derived hesperornithines and Apsaravis); pisiform process on carpometacarpus (unknown in Patagopteryx and Hongshanornis); supratrochlear fossa deeply excavating proximal surface of pisiform process (unknown in more basal euornithines sensu Sereno); anterior cnemial crest present (also in Archaeorhynchus); medial tibiotarsal condyle narrower than lateral condyle (absent in Enaliornis? sedgwicki); well developed lateral and medial crests on posterodistal tibiotarsus defining sulcus cartilaginis tibialis (unknown in more basal euornithines sensu Sereno); proximal metatarsal III displaced plantarily.

Longicrusavis O'Connor, Gao and Chiappe, 2010
L. houi O'Connor, Gao and Chiappe, 2010
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype
- (PKUP V1069) skull (30.7 mm), mandibles, hyoid, seven cervical vertebrae, two anterior dorsal vertebrae, two dorsal vertebrae, several dorsal vertebrae, dorsal ribs, synsacrum, incomplete scapulae (23.1 mm), coracoids (12.7 mm), incomplete furcula (~12.7 mm), partial sternum, humeri (26 mm), radii (24 mm), ulnae (25 mm), radiale, ulnares, carpometacarpi (one incomplete; 13.1 mm, mcI ~2.7 mm, mcII 11.5 mm, mcIII 11.1 mm), phalanx I-1 (6.9 mm), manual ungual I (4.3 mm), phalanges II-1 (7 mm), phalanges II-2 (7.3 mm), manual unguals II (3.4 mm), phalanges III-1 (3.2 mm), phalanges III-2 (0.8 mm), incomplete ilium, incomplete pubes (~31 mm), ischia, femora (24.3 mm), tibiotarsi (37.6 mm), fibulae (~16.6 mm), metatarsal I (4 mm), phalanx I-1 (4.1 mm), pedal ungual I (3.3 mm), tarsometatarsi (one incomplete; 21.5 mm, mtII 19.2, mtIII 21 mm, mtIV 19.6 mm), phalanx II-1 (6.3 mm), phalanx II-2 (5.4 mm), pedal ungual II (3.3 mm), phalanx III-1 (6.8 mm), phalanx III-2 (5.7 mm), phalanx III-3 (5.1 mm), pedal ungual III, phalanx IV-1 (~4 mm), phalanx IV-2 (4.1 mm), phalanx IV-3 (3.7 mm), phalanx IV-4 (3.8 mm), pedal ungual IV (3 mm), body feathers, remiges
Diagnosis- (after O'Connor et al., 2010) robust beak (relative to Hongshanornis); posteromedial sternal process absent; dorsal supracondylar process present on distal humerus; lateral cnemial crest hooked; second and fourth metatarsals subequal in length.
(suggested) premaxilla makes up at least half of facial margin (also in Ichthyornis+Passer); dorsal pleurocoels present; deltopectoral crest projected anteriorly (also in Patagopterygidae and Aves); medial tibiotarsal condyle <60% the width of the lateral condyle (also in Apsaravis); tibiotarsal condyles do not slope towards center in distal view (also in Apsaravis); m. tibialis cranialis tubercle placed medially on metatarsal II.
Comments- This taxon is a hongshanornithid in O'Connor et al.'s (2009, 2010) trees, but this is problematic as noted in the comments under Hongshanornithidae. In my trees it is sister to the Songlingornithidae+Aves clade, but this is provisional as the only information I've incorporated so far are O'Connor et al.'s codings.
References- O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.
O’Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.

unnamed clade (Songlingornis linghensis + Passer domesticus)
Diagnosis- (proposed) premaxillary teeth absent anteriorly (also in Archaeorhynchus and Hongshanornis); ten or less dorsal vertebrae (unknown in Longicrusavis); transverse groove present on humerus (also in Alamitornis; absent in Aves);

Songlingornithidae Hou, 1997
Definition- (Songlingornis linghensis <- Chaoyangia beishanensis, Passer domesticus) (Martyniuk, 2012)
= Yanornithiformes Zhou and Zhang, 2001
Definition- (Yanornis martini <- Passer domesticus) (Martyniuk, 2012)
= Yanornithidae Zhou and Zhang, 2001
= Yixianorniformes Zhang and Zhou, 2006
= Yixianornithidae Zhang and Zhou, 2006
Diagnosis- (after Clarke et al., 2006) posteromedial sternal process joins distally to posteromedian process forming fenestra.
(after Zhou and Zhang, 2006) femoro-tarsometatarsal ratio ~150-170%.
(proposed) pointed omal tips of furcula (also in Archaeorhynchus); bicipital crest lacks fossae (also in Patagopteryx and derived hesperornithines); dorsal ulnar cotyla not convex (also in Gansus).
Other diagnoses- Clarke et al. (2006) found four characters to unambiguously diagnose this clade. Archaeorhynchus and Gansus are now known to also lack completely heterocoelous cervicals, making it more parsimonious to be a plesiomorphy that was changed convergently in Patagopteryx and more derived birds. Similarly, a procoracoid process is now known in the more basal Archaeorhynchus, Hongshanornis and another unnamed Jiufotang taxon, making it more parsimonious to be lost in Patagopteryx and Apsaravis than to be primitive for ornithuromorphs and convergently evolved in songlingornithids. The lack of a medially concave coracoid surface (where the supracoracoid foramen exits if it is present) is more parsimoniously primitive to Ornithothoraces, as it is present in Longirostravis and Gansus, while the concavity in Apsaravis and hesperornithines are considered reversals.
Zhou and Zhang's (2006) diagnosis for Yixianornis' eponymous family and order was the same as their 2001 diagnosis for the genus. Most of those characters are apomorphic for Yixianornis or otherwise problematic (see Yixianornis diagnosis), except the femoro-tarsometatarsal ratio.
Comments- Hou (1997) originally named Songlingornithidae for Songlingornis within the Chaoyangiformes. Zhou and Zhang (2001) later named Yanornithidae and Yanornithiformes for Yanornis, while placing Yixianornis in Chaoyangornithiformes. Zhou and Zhang (2006) created Yixianornithidae and Yixianornithiformes for Yixianornis, and placed Songlingornis in the Chaoyangornithiformes and "Chaoyangornithidae". Clarke et al. (2002) were the first to suggest placing the three taxa into a single clade at their SVP talk, though this was not published until 2006. You et al. (2006) independently coded Yanornis and Yixianornis and found the taxa to form a monophyletic clade in some of their most parsimonious trees, though in others Yanornis was more derived and sister to Apsaravis. The monophyletic clade of Yanornis, Yixianornis and/or Songlingornis has been called Songlingornithidae by recent authors such as Martyniuk (2012) and O'Connor and Zhou (in press).
References- Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp.
Zhou and Zhang, 2001. [Two new genera of ornithurine birds from the Early Cretaceous of Liaoxi involved in the origin of modern birds.] Kexue Tongbao. 46(5), 371-377.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Yanornis Zhou and Zhang, 2001
= "Archaeoraptor" sensu Sloan, 1999 in part
= Archaeovolans Czerkas and Xu, 2002
Y. martini Zhou and Zhang, 2001
= "Archaeoraptor liaoningensis" Sloan, 1999 in part
= Archaeovolans repatriates Czerkas and Xu, 2002
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China

Holotype- (IVPP V12558) (~275 mm) skull (65 mm), mandibles, hyoid, ten cervical vertebrae, several dorsal vertebrae (6.3 mm), five dorsal ribs, gastralia?, synsacrum (38 mm), pygostyle, scapulae (~55 mm), coracoids (30 mm), furcula, sternum (48.4 mm), humeri (77.7 mm), radii (75.7 mm), ulnae (79.6 mm), radiale, ulnare, carpometacarpus (35 mm, mc I 6.4 mm, mc II 31 mm, mc III 31 mm), phalanx I-1 (17.2 mm), manual ungual I (8.1 mm), phalanx II-1 (17 mm), phalanx II-2 (17 mm), manual ungual II (7 mm), phalanx III-1, ilia, pubes (~67 mm), ischium, femora (52 mm), tibiotarsi (79.3 mm), fibulae (32 mm), metatarsals I (6 mm), phalanges I-1 (8.6 mm), pedal unguals I (5 mm), tarsometatarsi (38 mm), phalanges II-1 (14.3 mm), phalanx II-2 (11.9 mm), pedal ungual II (6 mm), phalanx III-1 (14.6 mm), phalanx III-2 (11 mm), phalanx III-3 (10 mm), pedal ungual III (6 mm), phalanges IV-1 (9 mm), phalanges IV-2 (6 mm), phalanges IV-3 (6 mm), phalanges IV-4 (6 mm), pedal unguals IV (5 mm)
Paratype- (IVPP V10996) incomplete skeleton
Referred- (IVPP V12444; specimen of "Archaeoraptor liaoningensis" in part; holotype of Archaeovolans repatriates) incomplete skull (~60 mm), partial mandibles, hyoid, several cervical vertebrae, few dorsal vertebrae (6.4 mm), several dorsal ribs, synsacrum, partial scapulae (57 mm), partial coracoids (38 mm), furcula (23 mm), sternum (48.2 mm), sternal ribs, humeri (~78.4 mm), radii (72.7 mm), ulnae (78.1 mm), radiale, ulnare, distal carpal III, carpometacarpi (one partial; mc I 7 mm, mc II ~36.9 mm), phalanx I-1 (~17 mm), manual ungual I (8 mm), phalanges II-1 (one partial; 17 mm), phalanges II-2 (18 mm), manual unguals II, phalanx III-1, partial ilia, proximal pubis, ischium, femur (~66 mm), tibiotarsus (78.1 mm), fibula, phalanx I-1 (8.4 mm), tarsometatarsus (38.8 mm), phalanx II-1 (14.1 mm), phalanx II-2 (12.1 mm), phalanx III-1 (14.7 mm), six pedal phalanges, three pedal unguals, body feathers, remiges (Sloan, 1999)
(IVPP V13259) specimen including dorsal vertebrae, dorsal ribs, sternum and femur (Zhou et al., 2002)
(IVPP V13278) partially or completely articulated specimen (Zhou et al., 2004)
(IVPP V13358) skull, mandibles, hyoid, seven cervical vertebrae, several dorsal vertebrae, several dorsal ribs, gastralia, sacrum, two proximal caudal vertebrae, scapulae, coracoids, furcula, sternum, humeri, radii, ulnae, radiale, ulnare, carpometacarpi, phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, manual unguals II, phalanx III-1, ilium, pubes, ischium, femur, tibiotarsi, tarsal?, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi, phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, gastroliths (<2 to 2.7 mm), body feathers (Zhou et al., 2004)
(LHZA02-0008) partial skull (61.9 mm), anterior dentary, eighth cervical vertebrae, three dorsal vertebrae, fragmentary synsacrum (34.5 mm), scapulae (49.5 mm), coracoid (30.3 mm), furcula, humeri (70.1 mm), radii (69.4 mm), ulnae (70.2 mm), radiale, ulnare, carpometacarpi (mc I 5.5 mm, mc II 30 mm, mc III 29 mm), phalanges I-1 (15.5 mm), manual unguals I (8.5 mm), phalanges II-1 (16.3 mm), phalanges II-2 (15.8 mm), manual unguals II (7 mm), phalanx III-1 (8 mm), pubes (51.4 mm), ischium (20 mm), femora (53 mm), tibiotarsi (68.7 mm), fibula (19 mm), metatarsal I, phalanx I-1 (8.2 mm), pedal unguals I (5.5 mm), tarsometatarsi (35.5 mm), phalanges II-1 (13 mm), phalanges II-2 (10.3 mm), phalanges II-3 (9.5 mm), pedal unguals II (6.2 mm), phalanges III-1 (13.5 mm), phalanges III-2 (10.7 mm), phalanges III-3 (9.8 mm), pedal unguals III (7.5 mm), phalanges IV-1 (9.7 mm), phalanges IV-2 (9.3 mm), phalanges IV-3 (7.1 mm), phalanges IV-4 (6.1 mm), pedal unguals IV (5 mm) (Yuan, 2004)
Diagnosis- (after Zhou and Zhang, 2001) forelimb/hindlimb ratio (hum+uln+carp/fem+tib+tars) 106-114%.
(after Clarke et al., 2006) humerus longer than scapula (also in Gansus and Hesperornis regalis).
(proposed) caudal zygapophyses unreduced (unknown in other songlingornithids; also in Ichthyornis); laterally hooked acromion process (also in Apsaravis); medially hooked acrocoracoid process (also in Ichthyornis and Songlingornis); ventroposterior surface of radius with longitudinal groove(?); metatarsal II not ginglymoid (also in some hesperornithines and Apsaravis).
Other diagnoses- Zhou and Zhang (2001) listed several additional characters in their diagnosis. A straight dentary is also present in Songlingornis, Ichthyornis and hesperornithids. According to their figure, the dentary is only 43% of skull length (which is similar to other basal ornithuromorphs), not 66%. The number of dentary teeth (20) is similar to Ichthyornis (21-24). Elongate cervical vertebrae are also present in Patagopteryx, hesperornithines and ambiortiforms. While stated to be hetercoelous by Zhou and Zhang (2001), the cervicals were coded as semihetercoelous by Zhou and Zhang (2005) and amphicelous by Clarke et al. (2006). Their true state remains to be determined. A synsacrum with nine vertebrae is also known in Yixianornis and Patagopteryx. The supposed short pygostyle lacks identifying features and may be another element (Senter, pers. comm.). Posterior sternal fenestrae are present in Yixianornis and Songlingornis as well. The posterolateral sternal process is not distally semicircular, but rather slightly convex as in Yixianornis and Archaeorhynchus. The manus is shorter than the ulna, but contra Zhou and Zhang is not shorter than the radius. In any case, the carpometacarpo-ulnar ratio (43-47%) is very similar to Yixianornis (42%), Patagopteryx (44%), Archaeorhynchus (45%), and Gansus (48%). The tarsometatarsus is completely fused in all ornithuromorphs. The third pedal digit is similar in length (109-117% of tarsometatarsal length) to Patagopteryx (~106%) and Gansus (102-116%). Proximal pedal phalanges are longer and more robust than distal phalanges in other basal ornithuromorphs where known.
Czerkas and Xu (2002) diagnosed Archaeovolans based on several characters. The number of premaxillary teeth (four) is plesiomorphic, as is them being larger than dentary teeth. The large number of dentary teeth (at least eighteen) is dealt with above. While they claim uncinate processes were absent, the ribcage is only partially articulated and has several small transverse elements which could be uncinates. The "strikingly modern" pectoral girdle is vague but is shared with more derived birds in any case. The supposedly short sternal keel as illustrated is not present in the specimen, which shows an elongate keel as in other Yanornis specimens and basal ornithuromorphs. The radiale and ulnare are said to be "well developed", but this is vague and they are comparable to other basal ornithuromorphs. The lack of a long ventral ramus is plesiomorphic and shared with Yixianornis and Gansus. Finally, the lack of a projected ventral carpal trochlea is plesiomorphic and shared with other basal ornithuromorphs such as Yixianornis and Patagopteryx.
The "Archaeoraptor" debacle- The specimen IVPP V12444 was fraudulently combined with the tail of the Microraptor zhaoianus holotype by a Chinese farmer. It was smuggled out of the country then sold at the 1998 Tuscon Gem Show to Czerkas. Currie recognized the legs were part and counterpart slabs of the same bones, while Rowe and Aulenback independently verified the composite nature of the specimen. National Geographic announced the specimen in a press conference in October, and in November, Sloan (1999) published a paper using the name "Archaeoraptor liaoningensis". This was a nomen nudum because it explicitely stated the taxon was to be described formerly in an official publication. That official publication was to have been in Science or Nature, but both journals rejected it. In April, Olson (2000) published an article purporting to officially describe "Archaeoraptor" and attach that name to the dromaeosaurid tail (with the latter as the lectotype). Several months later in December, Xu et al. (2000) officially named Microraptor zhaoianus based on the dromaeosaurid tail and associated anterior part of the skeleton Xu had discovered. At this time, Olshevsky (DML, 2000) noted that Olson's publication predated Xu et al.'s, and he believed that this made Microraptor a junior synonym of "Archaeoraptor". Several days later, Creisler (DML, 2001) pointed out the Olson's attempt to name "Archaeoraptor" was invalid because the ICZN requires a diagnosis in a valid publication, while Olson merely referenced the invalid article by Sloan. Creisler further indicated Olson cannot designate a lectotype without a valid publication defining a holotype first. Thus "Archaeoraptor" is still a nomen nudum, despite Olson's efforts, and Microraptor zhaoianus is the valid name for the IVPP V 12330 dromaeosaurid. The specimen was returned to the IVPP in May, 2000 and Zhou and Zhang were asked to work on the ornithuromorph section. They noticed the similarity with Yanornis shortly before completing their paper on that taxon in December 2000. Rowe et al. (2001) detailed the composite nature of the specimen, recognizing it was from at least two, and possibly up to five animals. They noted the ornithuromorph section (IVPP V 12444) was to be described by Xu (in prep.), which later appeared as Czerkas and Xu (2002). These authors described the specimen as a new taxon of ornithurine bird- Archaeovolans repatriates. Czerkas and Xu noted in an addendum that the recently described Yanornis martini was extremely similar and might be congeneric, though they also thought differences were present. Zhou et al. published their work in 2002, noting that both anatomy and proportions were nearly identical in the holotypes for the two species and synonymized them. While Rowe et al. found no evidence the right femur and both tibiotarsi, fibulae and pes belong to the same individual as the body, Zhou et al. (2002) confirmed they do.
Miscoded originally? Zhou and Zhang (2005) were the first authors to code Yanornis, but You et al. (2006) changed numerous codings based on personal observation of the holotype by Chiappe and O'Connor. Clarke et al. (2006) later coded Yanornis again based on the holotype, IVPP V12444, V13259 and V13358. These include making the following states uncertain- anterior premaxillary fusion (stated to be present by Zhou et al., 2002 and coded so by Clarke et al.); fusion of frontoparietal suture (appears absent in the figure of the holotype; also uncertain in Clarke et al.); quadrate pneumaticity including cluster of foramina on dorsal process (also uncertain in Clarke et al.); presence of external mandibular fenestra (appears absent in the figure of the holotype; also uncertain in Clarke et al.); coely of cervical vertebrae (stated to be heterocoelous by Zhou and Zhang, 2001; coded as semihetercoelous by Zhou and Zhang, 2005; coded as amphicoelous by Clarke et al.); presence of large hypapophyses on mid dorsal vertebrae (appears absent in IVPP V12444; coded as absent by Clarke et al.); number of dorsal vertebrae (also uncertain in Clarke et al.); presence of notarium (seems absent from figures of holotype and IVPP V12444; coded as absent by Clarke et al.); number of sacral vertebrae (stated to be and illustrated as nine by Zhou and Zhang, 2001; coded as nine by Clarke et al.); number of sacrals with dorsally directed diapophyses (stated to be and illustrated as none by Zhou and Zhang, 2001; coded as none by Clarke et al.); length and presence of pygostyle (the supposed pygostyle of the holotype has no features identifying it as such- Senter, pers. comm.); median proximity of coracoid sulci on sternum (coded as close or overlapping by Clarke et al.); presence of intermuscular lines on sternum (also uncertain in Clarke et al.); lateral excavation of furcula (coded as absent by both Clarke et al. and Nesbitt et al., 2009); pointed epicleidea (coded as absent by both Clarke et al. and Nesbitt et al., 2009; but seemingly present in IVPP V12444 and V13358); concavity of dorsal coracoid surface (stated to be deeply concave distally by Zhou and Zhang, 2001; coded as flat by Clarke et al.); pneumaticity of coracoid (coded as absent by Clarke et al.); position of glenoid relative to acrocoracoid (stated to be ventral by Czerkas and Xu and coded as such by Clarke et al.); curvature of acrocoracoid (coded as medially hooked by Clarke et al.); presence of supracoracoid foramen (also uncertain in Clarke et al.); whether the supracoracoid foramen opens into a medial groove (unknown since the foramen's presence is uncertain); angle between scapula and coracoid (less than 90 degrees in IVPP V13358; coded as such by Clarke et al.); length of acromion (illustrated as long in the holotype, but as short in IVPP V12444 and V13358; coded as long by Clarke et al.); curvature of acromion (stated to be curved by Zhou et al., 2002; coded as straight by Clarke et al.); presence and morphology of capital groove and ventral tubercle (also uncertain in Clarke et al.; all specimens seem to be preserved with humeri in anterior view); presence of anterior concavity on humeral head (actually already coded unknown by Zhou and Zhang, 2005; but coded absent by Clarke et al.); development of bicipital crest (stated to be ball-shaped by Zhou and Zhang, 2001 and well developed by Czerkas and Xu; coded as enlarged by Zhou and Zhang and moderate by Clarke et al.); presence of brachial fossa on humerus (also uncertain in Clarke et al.); demarkation of muscle origins on the dorsodistal humerus (also uncertain in Clarke et al.); presence of scapulotricipital and humerotricipital grooves (also uncertain in Clarke et al.; all specimens seem to be preserved with humeri in anterior view); separation of ulnar cotyla (also uncertain in Clarke et al.); semilunar morphology of dorsal ulnar condyle (visible in IVPP V12444; stated to be present by Zhou and Zhang, 2001 and coded as such by Clarke et al.); morphology of ventroposterior surface of radius (apparently grooved in both IVPP V12444 and V13358; coded as flat or scarred by Clarke et al.); length of ulnare rami (poorly developed in IVPP V12444 and coded as such by Clarke et al.); comparative lengths of dorsal and ventral ulnare rami (coded as subequal by Clarke et al.); width of metacarpal III (is approximately 50% in the holotype and IVPP V12444; seems much narrower in Zhou and Zhang's illustration of IVPP V13358, but is wider in the photo; coded as narrower by Clarke et al.); convexity of medial metacarpal I edge (concave in IVPP V12444; also coded uncertain in Clarke et al.); presence of internal index process of manual phalanx II-2 (absent in IVPP V13358 and coded as such by Clarke et al.); dorsal fusion of ilia (clearly absent in the holotype and coded as such by Clarke et al.); anterior extent of ilium (does not overlap last dorsal vertebra in the holotype and coded as such by Clarke et al.); presence of cuppedicus fossa on ilium (also coded uncertain in Clarke et al.); size and presence of posterior trochanter (also coded uncertain in Clarke et al.); fusion of tibiotarsus (coded as completely fused by Clarke et al.); comparative anterior projection of tibiotarsal condyles (also coded uncertain in Clarke et al.); presence of supratendinal groove (coded as absent by Clarke et al.); presence of retinaculi extensor tubercle on distal tibiotarsus (also coded uncertain in Clarke et al.); comparative width of tibiotarsal condyles (also coded uncertain in Clarke et al.); medial constriction of tibiotarsal condyles in distal view (coded as constricted by Clarke et al.); width of tibiotarsal intercondylar groove in distal view (coded as wide by Clarke et al.); extent of cartilaginous tibial sulcus (actually already coded unknown by Zhou and Zhang, 2005); distal tibiotarsal width compared to midshaft width (coded as subequal by Clarke et al., but this seems untrue in most birds including Yanornis, making interpretation of Clarke's character problematic); distal contact between fibula and tarsus (absent in all specimens; as coded by Clarke et al.); hypotarsal development (coded as absent or lacking crests and foramina by Clarke et al.); development of fossa for metatarsal I (also coded uncertain in Clarke et al.); ginglymoidy of metatarsal II (seems rounded in IVPP V13358); relative transverse width of metatarsals (subequal in IVPP V13358 and coded as such by Clarke et al.); number of distal vascular foramen exits in tarsometatarsus (also coded uncertain in Clarke et al.).
They also changed several codings- dentary symphysis without broad dorsally facing surface (which agrees with Czerkas and Xu, 2002); posterior dentary unforked (as it appears in the figure of the holotype); Meckelian groove not covered by splenial (which agrees with Czerkas and Xu, 2002); presence of lateral foramina in the dorsal centra (though described as pleurocoels by Zhou and Zhang and Czerkas and Xu, their size makes them more likely to be fossae as coded by Clarke et al.); lateral coracoid process absent (illustrated as present by Zhou and Zhang, 2001 and Zhou et al., 2002; coded as present by Clarke et al., 2006); ulna shorter than humerus (longer in specimens with exactly measured elements; as coded by Clarke et al.); dorsal ulnar cotyla not convex (coded uncertain by Clarke et al.); ulnar brachial scar present (also coded as present by Clarke et al.); intermetacarpal space reaches proximally to metacarpal I (present in all specimens; as coded by Clarke et al.); manual phalanx II-2 shorter than II-1 (coded as longer by Clarke et al., but actually varies from 97-106%, making it polymorphic); one proximal vascular foramen in tarsometatarsus (coded uncertain by Clarke et al.); metatarsal I straight (coded as curved by Clarke et al.); laterally placed m. tibialis cranialis tubercle on tarsometatarsus (as coded by Clarke et al.); metatarsal trochlea II subequal or wider than trochlea III and/or IV (Zhang and Zhou, 2001 state metatarsal II's trochlea is intermediate in width between III and IV; which state this represents is confusing, as Clarke's character has states compared to trochlea III AND/OR IV, so it agrees with parts of states 1 and 2); metatarsal II shorter than metatarsal IV, but reaching distally farther than base of metatarsal IV trochlea (as coded by Clarke et al; while Zhou and Zhang's illustration appears to show subequal lengths, their text states II is shorter).
Reffered specimens- The paratype (IVPP V10996) has yet to be illustrated or described. Zhou et al. (2002) noted a new specimen (IVPP V13259) which included macerated teleost vertebra, fin rays and opercular fragments and illustrated a small section of it. Yuan described another specimen which is notable in having four phalanges on each pedal digit II and a specimen of the osteoglossomorph Jinanichthys in its mouth. Zhou et al. (2004) briefly described a specimen with gastroliths (IVPP V13358), which was later illustrated by Zhou and Zhang, 2006, and mentioned another specimen (IVPP V13278).
References- Sloan, 1999. Feathers for T. rex?. National Geographic. 196(5), 98-107.
Olshevsky, DML 2000. http://dml.cmnh.org/2000Dec/msg00720.html
Olson, 2000. Countdown to Piltdown at National Geographic: the rise and fall of Archaeoraptor. Backbone, newsletter of the Department of Vertebrate Zoology, National Museum of Natural History. 13(2), 1-3.
Xu, Zhou and Wang, 2000. The smallest known non-avian theropod dinosaur. Nature. 408, 705-708.
Creisler, DML 2001. http://dml.cmnh.org/2001Jan/msg00092.html
Rowe, Ketcham, Deinson, Colbert, Xu and Currie, 2001. The Archaeoraptor forgery. Nature. 410, 539-540.
Zhou and Zhang, 2001. [Two new genera of ornithurine birds from the Early Cretaceous of Liaoxi involved in the origin of modern birds.] Kexue Tongbao. 46(5), 371-377.
Zhou and Zhang, 2001. Two new ornithurine birds from the Early Cretaceous of western Liaoning, China. Chinese Science Bulletin. 46(1), 1-7.
Czerkas and Xu, 2002. A new toothed bird from China. Feathered Dinosaurs and the Origin of Flight. 43-61.
Zhou, Clarke and Zhang, 2002. Archaeoraptor's better half. Nature. 420, 253-344.
Yuan, 2004. Further study of Yanornis martini (Ornithurae) from the Mesozoic Jehol Biota in Western Liaoning, China. Acta Geologica Sinica. 78(4), 464-467.
Zhou, Clarke, Zhang and Wings, 2004. Gastroliths in Yanornis: an indication of the earliest radical diet-switching and gizzard plasticity in the lineage leading to living birds? Naturwissenschaften. 91(12), 571-574.
Zhou and Zhang, 2005. Discovery of an ornithurine bird and its implication for Early Cretaceous avian radiation. Proceedings of the National Academy of Sciences. 102(52), 18998-19002.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Nesbitt, Turner, Spaulding, Conrad and Norell, 2009. The theropod furcula. Journal of Morphology. 270, 856-879.
Y. guozhangi Wang, Ji, Teng and Jin, 2013
Barremian-Aptian, Early Cretaceous
Yixian Formation, Liaoning, China

Holotype- (xhpm1205) skull (55 mm), mandibles, hyoids, cervical series, several dorsal vertebrae, dorsal ribs, uncinate processes, synsacrum (32 mm), few caudal vertebrae, pygostyle (12 mm), partial scapulae (45 mm), coracoid, furcula, sternum, humeri (72 mm), radii (74 mm), ulnae (74 mm), ulnare, carpometacarpi (36 mm), phalanges I-1 (19 mm), manual unguals I (10 mm), phalanges II-1 (15 mm), phalanges II-2 (15 mm), manual unguals II (6 mm), phalanges III-1 (8 mm), ilia, pubes (75 mm), ischia, femora (55 mm), tibiotarsi (68 mm), fibulae (44 mm), metatarsals I, phalanges I-1 (7 mm), pedal unguals I (5 mm), tarsometatarsi (33 mm), phalanges II-1 (12 mm), phalanges II-2 (10 mm), pedal unguals II (6 mm), phalanges III-1 (14 mm), phalanges III-2 (10 mm), phalanges III-3 (8 mm), pedal unguals III (6 mm), phalanges IV-1 (9 mm), phalanges IV-2 (7 mm), phalanx IV-3 (6 mm), phalanx IV-4 (6 mm), pedal ungual IV (5 mm), three fish
Diagnosis- (after Wang et al., 2013) large and strong deltopectoral crest, almost half length of shaft; symphysis <1/6 pubic length; fibula 2/3 length of tibiotarsus; tarsometatarsus completely fused and less than half tibiotarsal length.
Reference- Wang, Ji, Teng and Jin, 2013. A new species of Yanornis (Aves: Ornithurae) from the Lower Cretaceous strata of Yixian, Liaoning Province. Geological Bulletin of China. 32(4), 601-606.

unnamed clade (Yixianornis grabaui + Songlingornis linghensis)
Diagnosis- (proposed) dentary forked posteriorly (also in Apsaravis); supracoracoid foramen penetrates coracoid (unknown in Yanornis; also in Ichthyornis+Passer);

Yixianornis Zhou and Zhang, 2001
Y. grabaui Zhou and Zhang, 2001
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China

Holotype- (IVPP V12631) (~215 mm) skull (~39 mm), mandibles, sclerotic ring, atlas, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, ninth cervical vertebra, tenth cervical vertebra, eleventh cervical vertebra, twelfth cervical vertebra, ten dorsal vertebrae (5.8 mm), dorsal ribs, uncinate processes, fifteen rows of gastralia, synsacrum (25 mm), five caudal vertebrae, pygostyle, scapulae (48.1 mm), coracoids (23.3 mm), furcula, sternum (43.1 mm), sternal ribs, humeri (49.3 mm), radii (48 mm), ulnae (50.3 mm), radiale, ulnares, carpometacarpi (mc I 5 mm, mc II 21 mm, mc III 21 mm), phalanges I-1 (10.8 mm), manual unguals I (6.1 mm), phalanges II-1 (12.5 mm), phalanges II-2 (12.3 mm), manual unguals II (5 mm), phalanges III-1 (6 mm), ilia (23.5 mm), pubes (~42.2 mm), ischium (~20.5 mm), femora (41 mm), tibiotarsi (52.8 mm), fibula (~15 mm), metatarsal I (4 mm), phalanges I-1 (7.8 mm), pedal unguals I (5 mm), tarsometatarsi (27 mm), phalanges II-1 (11.3 mm), phalanges II-2 (9.4 mm), pedal unguals II (6 mm), phalanges III-1 (11.5 mm), phalanges III-2 (8.7 mm), phalanges III-3 (8.3 mm), pedal unguals III (6 mm), phalanges IV-1 (7 mm), phalanges IV-2 (5.8 mm), phalanges IV-3 (5.6 mm), phalanges IV-4 (6.2 mm), pedal unguals IV (5 mm), body feathers, eleven remiges (to 67 mm), eight retrices (~75-~92 mm)
Diagnosis- (after Zhou and Zhang, 2001) snout anterior to frontal margin of orbit 41% of skull length; metacarpal III 32% the width of metacarpal II (unknown in Songlingornis); pubic symphysis ~16% the length of pubis (unknown in Songlingornis); ratio of pedal digit III to tarsometatarsus length 128% (unknown in Songlingornis).
(proposed) basipterygoid processes absent (unknown in other songlingornithids); external mandibular fenestra present; distal coracoid laterally convex (also in Archaeorhynchus); no indication of muscle origins on dorsodistal edge of humerus (unknown in other songlingornithids; also in Apsaravis); m. scapulotriceps groove on posterodistal humerus (also in some Ichthyornis specimens); well developed bicipital tubercle on ulna (unknown in other songlingornithids; also in Ichthyornis and Apsaravis); extensor process present on metacarpal I (unknown in Songlingornis; also in Gansus+Passer);
Other diagnoses- Zhou and Zhang (2001) included a few other characters in their diagnosis. The short snout was expressed as a ratio of skull length to width (stated to be 150%, but in actuality 175% as preserved). However, the width is exaggerated by crushing the mandibles and jugals laterally, and the true ratio based on the postorbital processes is 235%. This makes it probably comparable to Hongshanornis, and Songlingornis is probably also short-snouted based on its dentary proportions, though difficult to quantify thanks to a lack of posterior skull material and good illustration. Clarke et al. (2006) use another measure of this feature, namely dentary length, which they state is shorter than in Songlingornis. One measure which can be compared in both Yixianornis and Hongshanornis is length anterior to the frontal margin of the orbit, which is shorter in Yixianornis (41% vs. 51%). It could be assumed Songlingornis' apparently longer dentary indicates it had a larger ratio. "Postcranial long bones slender" is unspecific and unquantified, but seems to be even more true of Hongshanornis and Gansus. Most ornithuromorphs have protruding elliptical humeral heads. While Zhou and Zhang use a pubic symphysis length of 20% pubic length in their diagnosis, their measurement table indicates a ratio of 26%, and Clarke et al.'s measurements indicate a smaller ratio of 16% (based on a pubis estimated to be 7 mm longer). While the proximal pubis is hidden by the femur, I find Clarke et al.'s estimate more likely based on the general length of basal bird pubic peduncles. The femoro-tarsometatarsal ratio (stated to be 160%, but actually 152%) is overlapped by Yanornis (149-170%).
Clarke et al. state the xiphoid process (just posterior to the costal margin) of the sternum has a greater extent along the sternal margin than in Yanornis or Songlingornis, but that of Hongshanornis and Gansus are longer (Songlingornis' seems to be also, at least in Hou's illustration). They also stated the interclavicular angle was longer than in Yanornis or Songlingornis, but this is also true in Hongshanornis, Archaeorhynchus and Gansus.
Comments- The holotype is misidentified as IVPP V13631 in Clarke et al.'s (2006) redescription. Their measurement of 12.5 mm for pedal phalanx IV-1 is also in error.
References- Zhou and Zhang, 2001. [Two new genera of ornithurine birds from the Early Cretaceous of Liaoxi involved in the origin of modern birds.] Kexue Tongbao. 46(5), 371-377.
Zhou and Zhang, 2001. Two new ornithurine birds from the Early Cretaceous of western Liaoning, China. Chinese Science Bulletin. 46(1), 1-7.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.

Songlingornis Hou, 1997
S. linghensis Hou, 1997
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype-
(IVPP V10913) (~190 mm) premaxilla, maxilla, nasals, quadrate, mandibles (25.5 mm), cervical vertebrae, several dorsal vertebrae, two dorsal ribs (31 mm), two dorsal rib fragments, scapula, coracoids (22.5 mm), furcula, sternum (35 mm), proximal radius, distal ulnae, carpometacarpus (25 mm), proximal femur, partial tarsometatarsus?
Diagnosis- (after Hou, 1997) dorsal edge of scapula almost straight.
(after Clarke et al., 2006) width of distal expansion of posterolateral sternal process 28% of sternal length.
(proposed) scapular expanded distally (also in Hesperornis regalis); medially hooked acrocoracoid process (also in Yanornis and Ichthyornis);
Other diagnoses- Hou (1997) included numerous characters in his diagnosis, but many are vague (mandible slender and elongate; ribs slender and elongate; well developed coracoid head; relatively well developed carpometacarpus; well developed femoral head) or primitive (dorsal vertebrae not heterocoelous; concave coracoid facet for scapula; procoracoid process present; supracoracoid foramen present; distal fossa on posterior coracoid; hypocleidium absent; elongate and broad sternum; deep coracoid grooves on sternum; distinct sternal carina). Others are found in other songlingornithids (teeth closely packed; more than nine dentary teeth; large anterolateral sternal process; well developed xiphoid sternal process; posterolateral sternal process with expanded tip; posterolateral sternal process extends posteriorly far beyond posteromedian process; posteromedial sternal process joins distally to posteromedian process forming fenestra).While Hou says the sternal rostrum ("manubrium") is well developed in the diagnosis, he later states it is damaged and cannot be described.
Zhou and Hou (2002) diagnose Chaoyangia partly using characters from Songlingornis. Most of the characters are repeated from Hou's earlier Songlingornis diagnosis. The remainder are plesiomorphic (premaxillary and dentary teeth present; U-shaped furcula; sternal keel extends along full length of sternum; short posterolateral sternal process).
Comments- This specimen was collected in 1992 and mentioned by Zhou (1995) as being probably referrable to Chaoyangia. Hou et al. (1995) say it is at least referrable to Ornithuromorpha (his Ornithurae), and later (1996) refer it to Chaoyangia due to the similar size and rarity of ornithuromorph birds in the deposits. Hou (1997) described it as the new taxon Songlingornis linghensis, while Zhou and Hou (2002) referred it to Chaoyangia but did indicate it had also been used as the holotype of Songlingornis. The holotypes of both specimens preserve few elements in common (though not none, as claimed by Clarke and Norell, 2001)- several dorsal vertebrae, dorsal ribs and proximal femur. The dorsals are alike in being non-heterocoelous, but this is similar to all non-hesperornithine, non-avian birds. Both femora are described as having proximally projecting trochanteric crests, shallow trochanteric fossae and large heads. These features are comparable to many basal birds including Confuciusornis and Vorona. The only point of difference in their descriptions in that Chaoyangia is said to have a "basically absent" neck, while Songlingornis has a "relatively well developed neck." Yet Chaoyangia's proximal femur has a near identical shape to Patagopteryx's, which has a neck, and Songlingornis' illustration is too schematic for proper comparison. Thus the taxa cannot be distinguished, but also share no synapomorphies that would allow them to be synonymized.
Songlingornis was originally described as a basal ornithuromorph (Ornithurae of Hou) by Hou (1997), placed on his phylogram more derived than Liaoningornis but less than Gansus and Ornithurae sensu Chiappe. Clarke (2002) was the first author to include the taxon in a cladistic analysis, finding it to be a carinate in an unresolved polytomy with Ichthyornis and more derived birds. More recently, Clarke et al. included Yanornis and Yixianornis in their matrix and found Songlingornis to clade with these taxa in a group more derived than Patagopteryx, but less than Apsaravis and Ornithurae sensu Chiappe. This was first announced at their SVP 2002 talk, but only published in 2006.
References- Hou, Zhou, Gu and Sun, 1995. Introduction to Mesozoic birds from Liaoning, China. Vertebrata PalAsiatica. 33(4), 261-271.
Zhou, 1995. New understanding of the evolution of the limb and girdle elements in early birds - evidences from Chinese fossils. In Sun and Wang (eds.). Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota. Short papers, 209-214.
Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: evidence from fossils from northeastern China. Science. 274, 1164-1167.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp.
Clarke and Norell, 2001. Fossils and avian evolution. Nature. 414, 508.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Zhou and Hou, 2002. The Discovery and Study of Mesozoic Birds in China. in Chiappe and Witmer, (eds.). Mesozoic Birds- Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 160-183.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.

unnamed clade (Gansus yumenensis + Passer domesticus)
Diagnosis- (proposed) some mid and posterior dorsal vertebrae with hypapophyses (absent in Ambiortus); gastralia absent; ten or more sacral vertebrae; extensor process present on metacarpal I (also in Yixianornis); preacetabular pectineal process; pubis subparallel to ilium; patellar groove present; extensor canal emarginate (absent in Enaliornis, E? sedgwicki and Apsaravis); fully twisted metatarsal I causing completely reversed hallux.

Changmaornis Wang, O'Connor, Li and You, 2013
C. houi Wang, O'Connor, Li and You, 2013
Early Aptian, Early Cretaceous
Xiagou Formation, Gansu, China

Holotype- (GSGM-08-CM-002) two dorsal vertebrae, dorsal rib, synsacrum, partial ilia, incomplete pubis, incomplete ischium, distal tibiotarsus, metatarsal I, phalanx I-1 (7.4 mm), pedal ungual I (3.9 mm), tarsometatarsus (36.9 mm), phalanx II-1 (10 mm), phalanx II-2 (9.9 mm), pedal ungual II (4.8 mm), phalanx III-1 (11.4 mm), phalanx III-2 (7.4 mm), phalanx III-3 (7.3 mm), pedal ungual III (4.2 mm), phalanx IV-1 (8.5 mm), phalanx IV-2 (6.3 mm), phalanx IV-3 (4.9 mm), phalanx IV-4 (4.9 mm), pedal ungual IV (3.6 mm)
Diagnosis- (after Wang et al., 2013) synsacrum composed of at least 11 sacral vertebrae with elongate distal transverse processes; ischium with dorsal process; distal half of the pubis compressed mediolaterally; metatarsal I J-shaped; distal margin of metatarsal II trochlea does not reach proximal margin of metatarsal III trochlea; pedal digit III longest in foot; ratio of pedal digit III to tibiotarsus 0.82; robust and blunt pedal unguals with poorly developed flexor tubercles.
Comments- Wang et al. entered this into O'Connor's matrix and found it to be a basal ornithomorph in large polytomy with taxa less derived than Ichthyornis but more derived than Patagopteryx.
Reference- Wang, O'Connor, Li and You, 2013. Previously unrecognized ornithuromorph bird diversity in the Early Cretaceous Changma Basin, Gansu Province, Northwestern China. PLoS ONE. 8(10), e77693.

Guildavis Clarke, 2004
Definition- (Guildavis tener <- Ichthyornis dispar, Struthio camelus, Tetrao major, Vultur gryphus) (modified from Clarke, 2004)
= "Guildavis" Clarke, 2002
G. tener (Marsh, 1880) Clarke, 2004
Definition- (the species that includes YPM 1760) (Clarke, 2004)
= Ichthyornis tener Marsh, 1880
= "Guildavis" tener (Marsh, 1880) Clarke, 2002
Cretaceous
Wallace County, Kansas, US

Holotype- (YPM 1760) partial synsacrum (~17 mm)
Other diagnoses- Clarke (2004) distinguished this taxon from Ichthyornis based on two characters. The first is the presence of parapophyses on the first sacral, which are also found in Gansus and Aves. The second is the presence of wider iliosacral sulci, but this is also seen in Patagopteryx, Gargantuavis, Zhyraornis and Gansus.
Comments- Marsh (1880) named this as a new species of Ichthyornis based on a synsacrum discovered in 1879, but never illustrated or described the species. He referred a distal humerus (YPM 1738) and coracoid (YPM 1766) to Ichthyornis tener without comment, but Clarke (2004) showed these are referrable to I. anceps (which she called I. dispar). Brodkorb (1967) incorrectly believed the humerus was YPM 1760, as Marsh never states which element YPM 1760 is and references a figure of the humerus. Clarke (2002) removed the holotype from Ichthyornis and described it as the new genus "Guildavis", which was published by her in 2004. Clarke noted Guildavis could not be compared to the probably contemporaneous Apatornis and Iaceornis besides being smaller, so may be synonymous with either of these taxa.
Clarke (2004) found Guildavis to be more derived than Ichthyornis based on the parapophysis on the first sacral, but this is now known to be present in the more basal Gansus as well. Similarly, Clarke found Guildavis to be excluded from Aves due to its amphicoelous anterior sacral articular surface, but some crown birds including most charadriiforms have this as well, and Clarke did not include any neoavians in her analysis.
References- Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Brodkorb, 1967. Catalogue of fossil birds: part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). Bulletin of the Florida State Museum (Biological Sciences). 11, 99-220.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT, 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.

Zhyraornithi Nessov, 1992
Zhyraornithidae Nessov, 1984
Zhyraornis Nessov, 1984
Diagnosis- (modified from Nessov, 1984) sacral centra four through eight extremely narrow ventrally (<30% of dorsal sacral width); well developed lateral fossa in second sacral centrum.
Comments- Of Nessov's (1984) other characters in his diagnosis- amphicoelous centra are symplesiomorphic for theropods; the sacrum's narrowness is similar to other basal carinates; the neural spine crest is continuous in most birds and is not tall in Z. logunovi; and the first sacral centrum has lateral fossae in Ichthyornis and Guildavis as well. Nessov's other characters are based on the questionably referred paratype dorsal (lateral central fossae in dorsal vertebrae) and scapula (curved and projected acromion).
Kurochkin (2000) included several additional characters in his diagnosis for the genus, but none are valid. Apatornis and many other Mesozoic birds have ventrally concave synsacra. The anterior articular surface is not particularily broad in Z. logunovi at least (width ~107% of height), comparable to the subcircular surfaces described for Ichthyornis and Guildavis. The slight anterior broadening is comparable to other basal carinates, as is the absence of a ventral groove. Ichthyornis can also only have one sacral with small transverse processes in front of those with large processes (in the holotype, but not YPM 1372). Finally, the largest transverse processes (on sacrals two and three) are also posteriorly directed in Ichthyornis.
Nessov (1984) first referred Zhyraornis to its own family within Ichthyornithiformes (in which he included Apatornis), due to the amphicoelous anterior articular surface and pleurocoels in the first two centra. While the latter seems to be based on incorrect homology with YPM 1372, Nessov was correct in his general idea. In 1992, he erected the suborder Zhyraornithi within Ichthyornithiformes, presumably to separate Zhyraornis further from Ichthyornis and Apatornis. Kurochkin (1995) suggested it was an enantiornithine, based on several characters and similarity to Gobipteryx (= Nanantius valifanovi of Kurochkin). Of the characters he lists, "flatness and general shape" are vague, but Zhyraornis has highly convex centra ventrally and the general sacral shape is almost identical to Apatornis. Contra Kurochkin, a ventral groove is absent in Zhyraornis, and pleurocoels are present anteriorly in Ichthyornis and Guildavis. In 1996, he elaborated his view, referring Zhyraornis to the Alexornithidae within Enantiornithes, again based on comparison to Gobipteryx. He referred it to Enantiornithes based on three characters. "General shortness" cannot be evaluated due to the missing posterior ends, but the taper of the sacrum and proportions of each vertebrae match Ichthyornis and Apatornis closely. The most anterior portion is said to have small, equisized transverse processes ventrally, but transverse processes two and three are much larger than the others, as in Apatornis and somewhat less in Ichthyornis (in the latter the third is largest, while the second is similar to the fourth). The wide neural canal is shared with all birds and most small maniraptoriforms. He referred it to Alexornithidae based on three characters. Dorsal curvature is also present in Apatornis and many other birds. Contra Kurochkin, the transverse processes are not equisized, being much larger in sacrals two and three, as noted above. Finally, he states only two or three costal processes are enlarged on the anterior synsacrum, but this is true in Apatornis, and is not necessarily true in Gobipteryx, as the anterior one or two sacrals are missing their lateral processes. Kurochkin later (2006) placed Zhyraornis in Ornithuromorpha based on unstated characters. In both his phylogram and cladogram, it is placed between Confuciusornithidae (which Kurochkin viewed as basal ornithuromorphs unrelated to dinosaurs, while enantiornithines were theropods) and Carinatae. His cladogram specifies a placement more derived than Liaoningornis, yet they share no known elements, so the result would be impossible in an actual phylogenetic analysis. His phylogram indicates indicates he believed it branched around Patagopteryx, Kuszholia and Gargantuavis.
Both species of Zhyraornis are similar in general morphology. The large lateral fossae on centra one and two are likely continuations of such fossae in the dorsal vertebrae, as seen in pygostylians. Z. kashkarovi's sacrum includes at least seven vertebrae, indicating they belong to Ornithothoraces or perhaps Oviraptorosauria. Yet oviraptorosaurs with seven sacrals differ in having all sacral vertebrae pleurocoelous, except Avimimus which has apneumatic centra and a ventral median groove. Sapeornis' sacrum is dissimilar in that the posterior transverse processes are most robust and the anterior three are directed anteriorly. Confuciusornis differs in having broader centra with a ventral groove and robust posterior transverse processes, though the anterior centra are similar in having pleurocoels. Most enantiornithines differ in having much broader centra with ventral grooves where known, and robust posterior transverse processes. The Lecho Formation enantiornithine PVL-4041-4 is roughly similar, although the first centrum is narrower and the fifth and sixth are broader. Also, the second and third transverse processes angle anteriorly instead of posteriorly, while those of the fourth, sixth and seventh vertebrae are more prominent. Gansus' is much broader after sacral two, with transverse processes two and three directed perpendicular or anteriorly and those of five and six more prominent. It seems to be similar in having fossae on sacral centra one and two though. Hesperornithines and neornithines differ in having a heterocoelous anterior articulation, while hesperornithines also differ in being non-pneumatic. Ichthyornis' sacrum is extremely similar in centrum width, transverse process size and direction, though the third transverse process is broader ventrally and the fourth better developed. Importantly, they share a series of midsacral reduced transverse processes, which is a carinate character. It is also similar in having pleurocoels on the first centrum, though seemingly not on the second. A complication is YPM 1372, which fused an extra dorsal to its sacrum, giving it two sacrals with pleurocoels. Yet the transverse process morphology in Zhyraornis suggests its first sacral is homologous to the second sacral in YPM 1372 and the first sacral in the Ichthyornis holotype. In Z. logunovi at least, the second transverse process is as robust as the third, unlike Ichthyornis. One major difference between Zhyraornis and Ichthyornis is that the centra of the former narrow drastically after the third centrum. Apatornis' is similar in being narrow and having a series of midsacrals with reduced transverse processes. The transverse process size and orientation are similar where known. Yet it differs from Zhyraornis in lacking a pleurocoel on sacral two (sacral one is not preserved), and apparently having less narrow centra ventrally, especially in the posterior centra (Nessov, 1984). Guildavis is similar in having narrow anterior centra without a ventral groove, and a pleurocoel on the first centrum. There may a be a pleurocoel in the second sacral as well, but if so it is smaller than Zhyraornis. Poor preservation presents further comparison. Which of these last three taxa Zhyraornis is more closely related to is unknown, as the total number of vertebrae, number of vertebrae with reduced transverse processes, and presence of parapophyses on the first vertebra are unknown. It is here assigned to Carinatae incertae sedis.
References- Nessov, 1984. [Upper Cretaceous pterosaurs and birds from Central Asia] Paleontologicheskii Zhurnal. 1, 47-57.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Kurochkin, 2006. Parallel evolution of theropod dinosaurs and birds. Entomological Review. 86(suppl. 1), S45-S58.
Z. kashkarovi Nessov, 1984
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype
- (TsNIGRI 42/11915) (~225 mm) anterior synsacrum (27 mm)
Diagnosis (after Nessov, 1984) neural spine crest on synsacrum tall.
(after Nessov, 1992) sacrum more concave ventrally than Z. logunovi or Apatornis; transverse processes in second and third sacrals with little projection in dorsal view; transverse processes of second and third sacrals extremely thin in ventral view.
(after Kurochkin, 2000) sacral centra four to eight <20% of dorsal width of sacrum.
Comments- Zhyraornis kashkarovi was first used in Nessov and Borkin (1983) as a figure caption for the dorsal vertebra TsNIGRI 43/11915, which was later made a paratype of the species. As no description accompanied the name, it was a nomen nudum. It may belong to Zhyraornis, as it seems to be an ornithothoracine but not an enantiornithine, hesperornithine or avian. It is given its own entry here, however. Nessov made additional specimens paratypes of Z. kashkarovi as well. The proximal scapula TsNIGRI 44/11915 is here referred to Ornithuromorpha incertae sedis, while the humeral shaft TsNIGRI 45/11915 is referred to Maniraptora indet.. Isolated shafts of long bones (TsNIGRI 48/11915, 49/11915 and 50/11915) which were not described or illustrated are similarly referred to Maniraptora indet..
The tall neural spine is the only one of Nessov's (1984) original diagnostic characters for Z. kashkarovi that is still valid at the species level. The others are dealt with under the genus entry. Nessov (1992) in his diagnosis of the new species Z. logunovi noted numerous differences, a few of which are apomorphic and are noted above.
Kurochkin (2000) listed a couple additional characters in his diagnosis. The slight anterior expansion of the first sacral centrum is indistinguishable from Guildavis. He notes the largest transverse processes (on sacrals two and three) are posteriorly angled (~55-60 degrees), but Ichthyornis shows this can be quite variable (~55-71 degrees in YPM 1372 and perhaps 86 degrees in the holotype), so this cannot be used to diagnose species. The sacrum does not appear more "extended" than in other basal carinates.
References- Nessov and Borkin, 1983. New records of bird bones from the Cretaceous of Mongolia and Soviet Middle Asia. USSR Academy of Sciences, Proceedings of the Zoological Institute. 116, 108-110 (in Russian).
Nessov, 1984. [Upper Cretaceous pterosaurs and birds from Central Asia] Paleontologicheskii Zhurnal. 1, 47-57.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Z. logunovi Nessov, 1992
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (PO 4600) (~200 mm) anterior synsacrum (~24 mm)
Diagnosis- (after Nessov, 1992b) wider anterior articular surface than Z. kashkarovi; pleurocoel in first sacral vertebra larger than Z. kashkarovi.
Comments- Of Nessov's (1992b) other listed diagnostic characters, the narrow sacrum with prominent ventral ridge is also present in Z. kashkarovi. The second sacral transverse process angles to be perpendicular to the sacrum long axis distally, which is indeed unlike Z. kashkarovi (unless it is broken in the latter), but is similar to Ichthyornis. The third sacral's transverse processes angle posteriorly ~69-78 degrees, which is less than Z. kashkarovi (~55-60 degrees), but Ichthyornis shows this can be quite variable (~55-71 degrees in YPM 1372 and perhaps 86 degrees in the holotype), so this cannot be used to diagnose species. The low amount of ventral concavity seem to be primitive, as Apatornis is similar. The more ventrally placed second vertebra's pleurocoel may be diagnostic, but the pneumatic features are known to exhibit a high degree of variation between individuals and even between sides of the vertebra. The well developed anterior transverse processes (in dorsal view) and wide ventral struts supporting them are plesiomorphically similar to Ichthyornis and Apatornis, though indeed dissimilar to Z. kashkarovi. Nessov stated the upper ridge behind the contact of the second and third sacrals was wider and better developed than in Z. kashkarovi, but I don't see a difference. Most of the spinal nerve foramina are said to be more anteroposteriorly compressed, but this is not apparent in the poor photocopy available and has unknown variation.
Kurochkin (2000) listed two additional characters in his diagnosis. The abrupt anterior expansion of the first sacral centrum is similar to Ichthyornis. The sacrum is not "generally expanded and broadened" for a carinate, only in comparison to the derived condition in Z. kashkarovi.
This specimen was discovered in 1989 and mentioned as a new species of Zhyraornis (though unnamed) by Mourer-Chauvire (1989) and Nessov (1992a). Kurochkin (1996) considered Z. logunovi to probably belong to a separate genus than Z. kashkarovi based on the characters described by Nessov, but they seem more similar to each other than to other Mesozoic birds, with the narrow posterior centra and lateral fossae on sacral centrum two being derived characters not present in Ichthyornis or Apatornis.
References- Mourer-Chauvire, 1989. Society of Avian Paleontology and Evolution Information Newsletter. 3.
Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. in Campbell (ed). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.

unnamed ornithuromorph (Buffetaut, Dyke, Suteethorn and Tong, 2005)
Valanginian-Barremian, Early Cretaceous
Sao Khua Formation, Thailand

Material- (K3-1) distal humerus
Comments- Possesses a brachial fossa, which is shared with carinates and Gansus, but not Patagopteryx or Apsaravis.
Reference- Buffetaut, Dyke, Suteethorn and Tong, 2005. First record of a fossil bird from the Early Cretaceous of Thailand. Comptes Rendus Palevol.

Gansuiformes Hou and Liu, 1984
Definition- (Gansus yumenensis <- Passer domesticus, Hesperornis regalis, Ichthyornis anceps, Enantiornis leali) (Martyniuk, 2012)
= Gansuidae Hou and Liu, 1984
= Gansuiornithiformes Zhou and Zhang, 2006
= "Gansuiornithidae" Zhou and Zhang, 2006
Comments- Zhou and Zhang (2006) listed Gansuiornithiformes and "Gansuiornithidae", which are incorrectly formed as there is no genus "Gansuiornis". Furthermore, "Gansuiornithidae" is a nomen nudum since it was not defined or diagnosed (ICZN Article 13.1.1).
References- Hou and Liu, 1984. A new fossil bird from Lower Cretaceous of Gansu and early evolution of birds. Scientia Sinica. 27, 1296-1302.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Gansus Hou and Liu, 1984
G. yumenensis Hou and Liu, 1984
Aptian-Albian, Early Cretaceous
Xiagou Formation, Gansu, China

Holotype- (IVPP V6862) (~250 mm) distal tibiotarsus, phalanx I-1 (8.4 mm), pedal ungual I (4.1 mm), phalanx II-1 (10.1 mm), tarsometatarsus (31.6 mm), phalanx II-2 (11.5 mm), pedal ungual II (5 mm), phalanx III-1 (13 mm), phalanx III-2 (10.8 mm), phalanx III-3 (8 mm), pedal ungual III (5 mm), phalanx IV-1 (11.1 mm), phalanx IV-2 (8.6 mm), phalanx IV-3 (8.4 mm), phalanx IV-4 (7.5 mm), pedal ungual IV (4 mm)
Referred- (CAGS-IG-04-CM-001) tibiotarsi (one distal; 63.7 mm), fibula, metatarsal I, phalanges I-1 (8.1 mm), pedal unguals I, tarsometatarsi (36.3 mm), phalanges II-1 (13.9 mm), phalanges II-2 (11.9 mm), pedal unguals II (5.2 mm), phalanges III-1 (14.2 mm), phalanges III-2 (9.4 mm), phalanges III-3 (8.7 mm), pedal unguals III (4.8 mm), phalanges IV-1 (12 mm), phalanges IV-2 (9.7 mm), phalanges IV-3 (9.4 mm), phalanges IV-4 (~9.4 mm), pedal unguals IV (4.9 mm) (You et al., 2006)
(CAGS-IG-04-CM-002) three posterior cervical vertebrae, (dorsal series 37 mm) ten dorsal vertebrae, three dorsal ribs, synsacrum (26.6 mm), (caudal series 15.6 mm) six caudal vertebrae, pygostyle (5.9 mm), ilia (38.2 mm), pubes (~49.1 mm), ischia (23.7 mm), femora (30 mm), tibiotarsi (one incomplete; 65.8 mm), fibulae, phalanx I-1 (8.2 mm), pedal ungual I (4.2 mm), tarsometatarsus (You et al., 2006)
(CAGS-IG-04-CM-003) few posterior cervical vertebrae, (dorsal series ~38 mm) ten dorsal vertebrae, dorsal ribs, synsacrum (26.9 mm), coracoids (21.7 mm), furcula, sternum (43.4 mm), sternal ribs, humeri (~48.4 mm), radii (one proximal), ulnae (one proximal; 52.8 mm), ulnare, carpometacarpus (25.2 mm), proximal phalanx I-1, phalanx II-1 (11 mm), phalanx II-2 (9.6 mm), phalanx III-1, ilia (34.6 mm), proximal pubes, proximal ischium, femur (31 mm), proximal tibiotarsus, proximal tarsometatarsus (You et al., 2006)
(CAGS-IG-04-CM-004) three posterior cervical vertebrae, (dorsal series 33.3 mm) ten dorsal vertebrae, dorsal ribs, synsacrum (29.2 mm), scapulae (41.7 mm), coracoids (19.2 mm), furcula, anterior sternum, sternal ribs, humeri (48 mm), radii (46.8 mm), ulnae (48.8 mm), radiales, ulnare, carpometacarpi (23.4 mm), phalanges I-1 (9 mm), manual unguals I (3.6 mm), phalanges II-1 (9.8 mm), phalanges II-2 (9.1 mm), manual unguals II (3.4 mm), ilia (33.4 mm), proximal pubis, proximal ischium (You et al., 2006)
(CAGS-IG-04-CM-008) dorsal rib, distal femur, tibiotarsus (53.4 mm), metatarsals I (4.52, 4.4 mm), phalanges I-1 (8.2, 8.19 mm), pedal unguals I (3.51, 3.88 mm), tarsometatarsi (32.04, 31.55 mm), phalanges II-1 (13.74, 13.4 mm), phalanges II-2 (10.81, 11.19 mm), pedal unguals II (4.46, 3.94 mm), phalanges III-1 (13.82, 14.19 mm), phalanges III-2 (8.88, 9.01 mm), phalanges III-3 (7.73, 7.65 mm), pedal unguals III (4.46, 4.42 mm), phalanges IV-1 (11.23, 10.98 mm), phalanges IV-2 (8.34, 8.39 mm), phalanges IV-3 (7.42, 7.35 mm), phalanges IV-4 (7.29, 7.30 mm), pedal unguals IV (4.18, 4.56 mm), scales (You et al., 2006)
(CAGS coll.) braincase fragment, anterior and mid cervical vertebrae (Harris et al., 2009)
(CAGS coll.) posterior skull, anterior and mid cervical vertebrae (Harris et al., 2009)
(CAGS coll.) posterior skull, anterior and mid cervical vertebrae (Harris et al., 2009)
(CAGS coll.) posterior skull, partial dentaries, anterior and mid cervical vertebrae (Harris et al., 2009)
(CAGS coll.) numerous specimens including about 70 partial to incomplete skeletons (Harris et al., 2009)
Diagnosis- (proposed) cervical centra amphicoelous (also in Archaeorhynchus and Ichthyornis); ossified uncinate processes absent; series of short sacral vertebrae, with dorsally directed parapophyses just anterior to the acetabulum (also in Ichthyornis and Aves); paired intermuscular ridges on sternum (also in Aves); humerus longer than scapula (also in Yanornis and Hesperornis regalis); pit-shaped fossa posteroventrally placed on bicipital crest; ventral condyle on humerus subequal or larger than dorsal condyle; dorsal ulnar cotyla not convex (also in Songlingornithidae); intermetacarpal space terminates distal to end of metacarpal I (also in Aves); preacetabular process overlaps a pair of dorsal ribs (also in Aves); capital ligament fossa absent on femur.
Comments- The holotype was discovered in 1981 and described by Hou and Liu (1984), who believed birds were divided into land and water clades, with Archaeopteryx ancrestral to the former and Gansus ancestral to the latter (except hesperornithines). Hou (1997) placed it sister to Ornithurae sensu Chiappe in his phylogram, and redescribed the taxon. Hope (2002) believed the specimen to be an ornithurine, but not an avian. Clarke (2002) coded the holotype for her matrix, finding it to be a carinate more derived than Ichthyornis, but less than Iaceornis and Aves. She noted the specimen was poorly preserved and "glued into the slab after being removed and repaired, obscuring almost all morphologies." You et al. (2005) coded the specimen for Chiappe's matrix and found it to be an ornithuromorph outside Ornithurae sensu Chiappe. You et al. (2006) describe several additional far more complete specimens of this genus, which they place as an ornithurine sensu Chiappe sister to Carinatae. Ji et al. (2006) later described one of the new specimens (CAGS-IG-04-CM-008) in detail, noting it preserves webbed feet. Harris et al. (2009) give preliminary data on more of the new specimens which include cranial elements, but these are not yet described.
References- Hou and Liu, 1984. A new fossil bird from Lower Cretaceous of Gansu and early evolution of birds. Scientia Sinica. 27, 1296-1302.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Zhou and Hou, 2002. The discovery and study of Mesozoic birds in China. in Chiappe and Witmer, (eds.). Mesozoic Birds- Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 160-183.
You, O'Connor, Chiappe and Ji, 2005. A new fossil bird from the Early Cretaceous of Gansu Province, northwestern China. Historical Biology. 17, 7-14.
Ji, Ji, You, Lu and Yuan, 2006. Webbed foot of an Early Cretaceous ornithurine bird Gansus from China. Geological Bulletin of China. 25(11), 1295-1298.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Harris, Lamanna, Li and You, 2009. Avian cranial material and cranial cervical vertebrae from the Lower Cretaceous Xiagou Formation of Gansu Province, China. Journal of Vertebrate Paleontology. 29(3), 111A.

Carinatae sensu Chiappe, 1995
Definition- (Ichthyornis dispar + Passer domesticus) (modified)
= Odontornithes Marsh, 1873
Definition- (Ichthyornis anceps, Hesperornis regalis <- Passer domesticus) (Martyniuk, 2012)
= Odontognathae Wetmore, 1930
= Ornithurae sensu Padian, 2004
Definition- (Hesperornis regalis + Ichthyornis dispar + Passer domesticus) (modified)
Diagnosis- premaxilla toothless (unknown in Gansus; also in Archaeorhynchus); premaxilla makes up at least half of facial margin (also in Longicrusavis); eustachian tubes ossified (unknown in other Ornithurae); quadrate head exposed laterally (unknown in Gansus and Songlingornithidae); pterygoid articulation of quadrate restricted to anteromedial edge of process (unknown in Gansus and Songlingornithidae); pterygoid articulation on quadrate does not reach tip of orbital process (unknown in Gansus and Songlingornithidae); Meckelian groove vovered medially by splenial (unknown in Gansus); lateral intermuscular line on ventral coracoid; supracoracoid foramen penetrates coracoid (absent in Ambiortus; also in Yixianornis+Songlingornis); dorsal surface of sternum pneumatic (unknown in other Euornithes sensu Sereno); m. humerotricipitalis groove on posterodistal humerus (unknown in Gansus); muscle impression along most of ventroposterior radius surface (unknown in Gansus); metacarpal III <50% width of metacarpal II (also in Yixianornis); intermetacarpal process present; pubic shaft transversely compressed; pubic symphysis absent (also in Patagopteryx); two proximal vascular foramina in tarsometatarsus (absent in Apsaravis); fossa for metatarsal I present on metatarsal II (unknown in Gansus).
Comments- Marsh (1873) named the new subclass Odontornithes for Ichthyornis. He later (1875a, b) included Hesperornis in Odontornithes as well, though in a separate order. Wetmore (1930) named Odontognathae as a superorder containing Hesperornithiformes and Ichthyornithiformes.
References- Marsh, 1873. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Wetmore, 1930. A systematic classification for the birds of the world. Proceedings of the US National Museum. 76(24), 1-8.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Horezmavis Nessov and Borkin, 1983
H. eocretacea Nessov and Borkin, 1983
Early Cenomanian, Late Cretaceous
Khodzhakul Formation, Uzbekistan

Holotype- (PO 3390) (~285 mm) proximal tarsometatarsus
Comments- Horezmavis was described as Aves (sensu lato) incertae sedis by Nessov and Borkin (1983), though Nessov later (1992) assigned it to Gruiformes based on resemblences to Ralli. Kurochkin (1995) considered it a gruiform based on several characters, but Hope (2002) found these to have a broader distribution within ornithuromorphs. Specifically, the position of the m. tibialis cranialis tubercle is shared with most ornithuromorphs as derived as songlingornithids; the intercotylar prominence is shared with Ichthyornis, derived hesperornithines and Aves basally; the presence of two proximal vascular foramina is present in Ichthyornis, Hesperornis and Aves; a hypotarsus is present in all ornithuromorphs; and an elongate shaft is also found in such taxa as Gansus, Hollanda, basal hesperornithines and Apsaravis. Kurochkin (2000) later stated its position within Gruiformes was less certain, but did feel it was a neognath. The characters he cites are also present in more basal ornithuromorphs however. A completely fused tarsometatarsus is present in all ornithuromorphs while a infracotylar fossa is present in songlingornithids and more derived birds. Martin (1995) considered it an enantiornithine, but this is surely incorrect based on the distal metatarsal fusion, proximal metatarsal III which is displaced ventrally, intercotylar priminence, hypotarsus, presence of two proximal vascular foramina, centrally placed m. cranialis tibialis tubercle, and unreduced metatarsal IV. The character evidence thus suggests it is at least as derived as Ichthyornis, but further resolution depends on more detailed comparisons to basal Aves.
References- Nessov and Borkin, 1983. [New records of bird bones from Cretaceous of Mongolia and Middle Asia] Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 116, 108-110.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Martin, 1995. The enantiornithines: terrestrial birds of the Cretaceous. Courier Forschungsinstitut Senckenberg. 181, 23–36.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.

unnamed ornithuromorph (Hope, 2002)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material
- (RTMP 93.116.1; Ornithurine F; Onefour bird) proximal coracoid
Comments- Hope (2002) referred this specimen to Cimolopteryx sp. based on unspecified features in her diagnosis of that genus. Longrich (2009) stated it differs from Cimolopteryx in lacking a strong convex ridge on the inside of the triosseal canal and having a quadrangular glenoid. He assigned it to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

unnamed ornithuromorph (Longrich, 2006)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada

Material- (RTMP 98.68.145) proximal carpometacarpus
Diagnosis- carpal fovea occupies entire proximal surface of metacarpal I; scar possibly for ulnare ligament present on dorsal surface of metacarpal II.
Comments- Longrich's phylogenetic analysis placed that taxon closer to Aves than Apsaravis, but further than Ichthyornis and Limenavis. It thus occupies the same position as hesperornithines (which have unpreserved carpometacarpi, but are known from the same formation), and may itself be a hesperornithine, as suggested by its diving adaptations (thick-walled bones; distally placed extensor process).
Reference- Longrich, 2006. An ornithurine bird from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 43, 1-7.

unnamed ornithuromorph (Longrich, 2009)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada

Material- (RTMP 86.112.6; Ornithurine A) partial coracoid
Comments- Longrich (2009) suggested the shallow scapular cotyle, massive shaft, and dorsally bowed shaft were similar to coracoids from the Ashville Formation of Saskatchewan which were originally referred to Ichthyornis spp., but which he believes are Pasquiaornis.
Reference- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

unnamed ornithuromorph (Longrich, 2009)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada

Material- (UALVP 47943) proximal coracoid
?(UALVP 47944) anterior sternum
?(UALVP coll.) sternum fragment
Comments- Longrich (2009) called this Ornithurine B or the Irvine bird. He assigned it to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet.
Reference- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

unnamed ornithuromorph (Longrich, 2009)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada

Material- (UALVP 47942; Ornithurine C) proximal coracoid
Comments- Longrich (2009) assigned this to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet, and noted it resembled Palintropus and Apsaravis in lacking a procoracoid process.
Reference- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

unnamed ornithuromorph (Longrich, 2009)
Late Campanian, Late Cretaceous
Oldman Formation, Alberta, Canada

Material- (RTMP 88.87.27; Ornithurine D; Devil's Coulee bird) partial coracoid
Comments- Longrich (2009) assigned this to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet.
Reference- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

unnamed ornithuromorph (Longrich, 2009)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada

Material- (RTMP 93.19.1; Ornithurine E; Steveville bird) proximal coracoid
Comments- Longrich (2009) assigned this to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet.
Reference- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

undescribed ornithuromorph (Longrich, 2009)
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Material- (BHI and SDSM coll.)
Comments- Longrich (2009) refers to a "large ornithurine" from the Lance Formation based on uncatalogued specimens at the BHI and SDSM.
Reference- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

Ichthyornithes Marsh, 1873b
Definition- (Ichthyornis dispar <- Struthio camelus, Tinamus major, Vultur gryphus) (Clarke, 2004)
= Ichthyornithidae Marsh, 1873a (emended Furbringer, 1888)
= Ichthyornithides Gill, 1874
= Odontotormae Marsh, 1875b
= Pteropappi Stejneger, 1885
= Ichthyornithiformes Furbringer, 1888
Definition- (Ichthyornis anceps <- Hesperornis regalis, Gansus yumenensis, Passer domesticus) (Martyniuk, 2012)
= Odontormae Steinmann and Doederlein, 1890
= Plegadornithidae Wetmore, 1962
= Angelinornithidae Kashin, 1972
Diagnosis- Currently identical to Ichthyornis dispar.
Other diagnoses- Marsh (1873a, b) originally diagnosed Ichthyornidae, Ichthyornithes and Odontornithes based on their amphicoelous vertebrae (only the posterior dorsals were definitely amphicoelous in Apatornis, based on its sacrum), which are plesiomorphic.
Marsh diagnosed Ichthyornithes (1875a) then Odontormae (1875b) by their plesiomorphic presence of teeth placed in sockets (as in most archosaurs), a keeled sternum (as in most ornithothoracines) and "developed wings" (as in most birds).
Comments- Marsh (1873a) named Ichthyornidae to include Ichthyornis and Apatornis, which Furbringer (1888) emended to its proper form Ichthyornithidae. Marsh later (1873b) placed ichthyornithids in the new order Ichthyornithes, but in the 1875b publication, replaced Ichthyornithes with Odontotormae because he thought the previous name was preoccupied. As Clarke (2004) noted though, Marsh never mentioned which taxon supposedly preoccupied Ichthyornithes, and recent searches for homonyms have been unsuccessful. Furbringer created Ichthyornithiformes for a more inclusive group than Ichthyornithes (though with the same known contents), which became the name generally used until Clarke phylogenetically defined Ichthyornithes in her Ichthyornis monograph. Clarke (2002) incorrectly claimed Furbringer never named the taxon and that it was only mistakenly attributed to him by Brodkorb. Wetmore (1962) named the Plegadornithidae for his new genus Plegadornis, which he placed in the Ciconiiformes close to threskiornithids. Kashin (1972) noted Plegadornis was preoccupied, so renamed it Angelinornis and suggested the family be named Angelinornithidae. Angelinornis was synonymized with Ichthyornis by Olson (1975), making Angelinornithidae a junior synonym of Ichthyornithidae. It should be noted Plegadornithidae should only be used for a family containing Plegadis however.
Ex-ichthyornithines- Marsh (1873a) included Apatornis in Ichthyornithidae and later Ichthyornithes and Odontotormae, which has been followed by most authors (based largely on Iaceornis material after 1880) until Clarke (2004) found a lack of supportive characters. Nessov (1984) assigned his new taxon Zhyraornis to Ichthyornithiformes, which may be correct but has not been supported with any valid characters yet. Nessov (1986) described a partial synsacrum as Ichthyornis maltshevskyi, but this was placed in the new genus Lenesornis by Kurochkin (1996) and seems to be a more basal ornithothoracine, perhaps an enantiornithine. Martin (1987) assigned Ambiortus to the Ichthyornithiformes, but it is probably a more basal ornithuromorph. Nessov (1990) described a dorsal vertebra as Ichthyornis minusculus, but this seems to be an enantiornithine (Kurochkin, 1996). Several specimens from the Bissekty Formation of Uzbekistan were assigned to Ichthyornithiformes by Nessov (1992a, b), but are here placed as Ornithothoraces incertae sedis (partial dentary PO 4608, tooth PO 4610, and posterior synsacrum) or Ornithuromorpha incertae sedis (proximal coracoid PO 4605, and dorsal vertebra PO 4607).
References- Marsh, 1873a. Notice of a new species of Ichthyornis. American Journal of Science, 3rd series. 5, 74.
Marsh, 1873b. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Gill, 1874. in Baird, Brewer and Ridgway. North American Birds. Volume 1.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Stejneger, 1885. Birds. in Kingsley (ed). The Standard Natural History. Volume 4.
Furbringer, 1888. Untersuchungeb zur Morphologie und Systematik der Vogel. Amsterdam: Holkema, 1751 pp.
Steinmann and Doederlein, 1890. Elemente der Palaontologie.
Wetmore, 1962. Notes on fossil and subfossil birds. Smithsonian Miscellaneous Collections. 145, 1-17.
Kashin, 1972. New name for the genus Plegadornis. Ornitologiya. 10, 336-337.
Olson, 1975. Ichthyornis in the Cretaceous of Alabama. Wilson Bulletin. 87, 103-105.
Nessov, 1984. [Upper Cretaceous pterosaurs and birds from Central Asia] Paleontologicheskii Zhurnal. 1, 47-57.
Nessov, 1986. Pervaya nakhodka pozdnemelovoy ptitsyikhtiornisa v starom svete i nekotoryye drugiye kosti ptits iz mela i paleogena Sredney Axii [The first find of the Late Cretaceous bird, Ichthyornis, in the Old World, and some other bird bones from the Cretaceous and Paleogene of Middle Asia]. in Potapov (ed). Ekologicheskiye i faunisticheskiye issledovniya ptits. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 147, 31-38.
Martin, 1987. The beginning of the modern avian radiation. Documents des Laboratoires de Geologie de la Faculte des Sciences de Lyon. 99, 9-20.
Nessov, 1990. Small Ichthyornis and other findings of the bird bones from the Bissekty Formation (Upper Cretaceous) of Central Kizylkum Desert. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 21, 59-62.
Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. in Campbell (ed). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Ichthyornis Marsh, 1872b
Definition- (the clade stemming from an ancestor that possessed amphicoelous cervical centra, an acromion that does not extend anteriorly past the coracoid condyle, a dorsal ulnar condyle where the posterior extent of the articular surface is equal to the width of the articular surface across its distal end, an oval scar on the posteroventral surface of the distal radius in the center of the ligamentous depression, and a large tubercle developed on the laterodistal surface of metacarpal II, homologous with those in Ichthyornis dispar; Ichthyornis dispar <- Struthio camelus, Tinamus major, Vultur gryphus) (Clarke, 2004)
= Colonosaurus Marsh, 1872c
= Plegadornis Wetmore, 1962 (preoccupied Brehm, 1855)
= Angelinornis Kashin, 1972
Comments- A number of other species have been referred to Ichthyornis in the past. Marsh (1873a) described Ichthyornis celer, but later referred it to its own genus Apatornis in 1873b. Marsh (1880) referred Graculavus lentus to Ichthyornis to form the new taxon Ichthyornis lentus, but this was placed in the new galliform genus Austinornis by Clarke (2002, 2004). Ichthyornis tener was named by Marsh (1880) and assigned to the new genus Guildavis by Clarke. Martin and Stewart (1982) described a dorsal vertebra from the Vermillion River Formation of Manitoba as Ichthyornis sp., but Clarke identified it as an enantiornithine. Nessov (1986) described a partial synsacrum as Ichthyornis maltshevskyi, but this was placed in the new genus Lenesornis by Kurochkin (1996) and seems to be a more basal ornithothoracine, perhaps an enantiornithine. Nessov (1990) described a dorsal vertebra as Ichthyornis minusculus, but this seems to be an enantiornithine (Kurochkin, 1996).
References- Brehm, 1855. Der vollständige Vogelfang. Weimar.
Marsh, 1873a. Notice of a new species of Ichthyornis. American Journal of Science, 3rd series. 5, 74.
Marsh, 1873b. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Wetmore, 1962. Notes on fossil and subfossil birds. Smithsonian Miscellaneous Collections. 145, 1-17.
Kashin, 1972. New name for the genus Plegadornis. Ornitologiya. 10, 336-337.
Martin and Stewart, 1982. An ichthyornithiform bird from the Campanian of Canada. Canadian Journal of Earth Sciences. 19, 324-327.
Nessov, 1986. Pervaya nakhodka pozdnemelovoy ptitsyikhtiornisa v starom svete i nekotoryye drugiye kosti ptits iz mela i paleogena Sredney Axii [The first find of the Late Cretaceous bird, Ichthyornis, in the Old World, and some other bird bones from the Cretaceous and Paleogene of Middle Asia]. in Potapov (ed). Ekologicheskiye i faunisticheskiye issledovniya ptits. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 147, 31-38.
Nessov, 1990. Small Ichthyornis and other findings of the bird bones from the Bissekty Formation (Upper Cretaceous) of Central Kizylkum Desert. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 21, 59-62.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
I. anceps (Marsh, 1872a) Marsh, 1880
= Graculavus anceps Marsh, 1872a
= Ichthyornis dispar Marsh, 1872b
Definition- (the species that includes YPM 1450) (Clarke, 2004)
= Colonosaurus mudgei Marsh, 1872c
= Graculavus agilis Marsh, 1873b
= Ichthyornis victor Marsh, 1876
= Ichthyornis agilis (Marsh, 1873) Marsh, 1880
= Ichthyornis validus Marsh, 1880
= Plegadornis antecessor Wetmore, 1962
= Angelinornis antecessor (Wetmore, 1962) Kashin, 1972
= Ichthyornis antecessor (Wetmore, 1962) Olson, 1975
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Holotype- (YPM 1208; holotype of Graculavus anceps) (~233 mm; adult) distal carpometacarpus
Referred- (AMNH 30586) skeleton (AMNH online)
(BMNH A905) partial postcranium including scapula, sternum and humerus (Harrison and Walker, 1973)
(FHSM VP-2179) distal tarsometatarsus (Everhart online, 2003-2007)
(FHSM VP-2503; = SMM 2503; "SMM 13520" of Martin and Stewart, 1977) partial dentary, splenial, five cervical vertebrae, scapula, coracoids, partial furcula, sternum, humeri, radius, proximal ulnae, ulnare, carpometacarpus, phalanx II-1, phalanx II-2, femoral shaft, incomplete tibiotarsus (Martin and Stewart, 1977)
(FSHM VP-15574) proximal coracoid (Everhart online, 2003-2009)
(FSHM VP-17317) incomplete coracoid (Everhart online, 2003-2007)
(KUVP 2294) humeral fragment (Chinsamy et al., 1998)
(KUVP 119673) incomplete postcranial skeleton including coracoids and humerus (Burnham and Hines, 2005)
(YPM 1209; holotype of Graculavus agilis) (size of YPM 1724; adult) proximal carpometacarpus (Marsh, 1873b)
?(YPM 1446) (adult) incomplete coracoid (Marsh, 1880)
(YPM 1447) (~292 mm; adult) humerus (71.1 mm) (Marsh, 1880)
(YPM 1450; holotype of Ichthyornis dispar; holotype of Colonosaurus mudgei) (~240 mm; adult) maxillary fragment, frontals, mesethmoid, braincase, mandibles (87 mm), posterior cervical vertebra (5.5 mm), posterior cervical vertebra (6 mm), mid dorsal vertebra (5.8 mm), posterior dorsal vertebra (6 mm), several proximal dorsal ribs, synsacrum (26.2 mm), ossified tendons, distal coracoid, anterior sternum, incomplete humeri (58.4 mm), distal radius, ulnae (61.5 mm), distal carpometacarpus, femur (24.7 mm), distal femur, incomplete tibiotarsus (44.5 mm), fragments (Marsh, 1872b, c)
(YPM 1452; holotype of Ichthyornis victor) (adult) proximal scapula, proximal coracoid, three humeral fragments (12.5 mm wide distally), ulna (lost) (Marsh, 1876)
(YPM 1453) (~288 mm; adult) ulna (73.8 mm) (Marsh, 1880)
(YPM 1454) (adult) ulna (Clarke, 2004)
(YPM 1456) (adult) distal tarsometatarsus (Marsh, 1880)
(YPM 1457) (adult) humerus (11 mm wide distally), radius, ulna (Marsh, 1880)
(YPM 1458) (adult) scapula, coracoid (Marsh, 1880)
(YPM 1459) (adult) premaxillary fragment, frontals, mesethmoid, braincase (Marsh, 1880)
(YPM 1460) (adult) ulna (Clarke and Chiappe, 2001)
(YPM 1461) (adult) dorsal ribs, coracoid, partial sternum, humerus (Marsh, 1880)
(YPM 1462) (adult) ulna (Clarke and Chiappe, 2001)
(YPM 1463) (adult) manual phalanx II-1 (21 mm) (Marsh, 1880)
(YPM 1464) (adult) distal tarsometatarsus (Marsh, 1880)
(YPM 1718) (adult) scapula, coracoid (Marsh, 1880)
(YPM 1719) (adult) coracoid (Clarke, 2004)
(YPM 1720) (adult) humerus (Clarke, 2004)
(YPM 1721) (adult) humerus (Clarke, 2004)
(YPM 1722) (adult) humerus (Clarke, 2004)
(YPM 1723) (adult) tibiotarsus (57 mm) (Marsh, 1880)
(YPM 1724) (adult) carpometacarpus (39.5 mm) (Marsh, 1880)
(YPM 1725) (adult) humerus (Clarke, 2004)
(YPM 1726) (adult) manual phalanx II-1 (20.8 mm) (Marsh, 1880)
(YPM 1727) (adult) scapula, coracoid (Marsh, 1880)
(YPM 1728) (adult) posterior nasals, frontals, mesethmoid (Clarke, 2004)
(YPM 1729) (adult) humerus (Clarke, 2004)
(YPM 1730) (~252 mm; adult) humerus (62.5 mm), carpometacarpus (31.5 mm) (Marsh, 1880)
(YPM 1731) (adult) ulna (Chiappe, 2002)
(YPM 1732) (adult) partial posterior dorsal vertebra, posterior dorsal vertebra, posterior dorsal vertebra, synsacrum, ossified tendons, first caudal vertebra (3.1 mm), second caudal vertebra (3.2 mm), third caudal vertebra (3.6 mm), fourth caudal vertebra (3.2 mm), fifth caudal vertebra (3.4 mm), anterior pygostyle, incomplete ilium, proximal pubis (26 mm), incomplete ischium, proximal femur, partial tibiotarsi (57 mm), pedal phalanx II-2 (9 mm) (Marsh, 1880)
(YPM 1733) (adult) atlas (2.7 mm), axis (7 mm), third cervical vertebra (6 mm), posterior cervical vertebra (6 mm), anterior dorsal vertebra (5.5 mm), anterior dorsal centrum, mid dorsal vertebra (6.7 mm), partial posterior dorsal vertebra, partial posterior dorsal centrum, posterior dorsal centrum, synsacrum, ossified tendons, scapula, incomplete coracoid, distal humerus, radius, partial ilium? (Marsh, 1880)
(YPM 1735) (adult) mandible (Marsh, 1880)
(YPM 1736) (adult) carpometacarpus (Chiappe, 2002)
(YPM 1737) (adult) humerus (Clarke, 2004)
(YPM 1738) (190-206 mm; adult) distal humerus (7.5 mm wide distally) (Marsh, 1880)
(YPM 1739) (adult) tarsometatarsus (58 mm) (Marsh, 1880)
(YPM 1740; holotype of Ichthyornis validus) (~267 mm; subadult) ulna (68.5 mm) (Marsh, 1880)
(YPM 1741) (adult) scapula, coracoid, humerus, radius (71 mm) (Marsh, 1880)
(YPM 1742) (~294 mm; adult) humerus (71.5 mm) (Marsh, 1880)
(YPM 1743) (adult) coracoid (34 mm) (Marsh, 1880)
(YPM 1744) (adult) ulna (Clarke, 2004)
(YPM 1745) (adult) coracoid (32 mm) (Marsh, 1880)
(YPM 1746) (adult) coracoid (Clarke, 2004)
(YPM 1747) (adult) humerus (Clarke, 2004)
(YPM 1748) (adult) humerus (Clarke, 2004)
(YPM 1749) (adult) mandible, partial humerus (Marsh, 1880)
(YPM 1750) (adult) humerus (Clarke, 2004)
(YPM 1751) (adult) carpometacarpus (Clarke, 2004)
(YPM 1752) (adult) carpometacarpus (Chiappe, 2002)
(YPM 1753) (adult) scapula (Chiappe, 2002)
(YPM 1754) (adult) distal tibiotarsus (Clarke, 2004)
(YPM 1755) (adult) furcular fragment, humerus (70.6 mm), radius, ulna, carpometacarpus (36.6 mm), manual phalanx II-1 (21.2 mm) (Marsh, 1880)
(YPM 1756) (~252 mm; adult) humerus (61.4 mm)
(YPM 1757) (adult) coracoid, humerus, ulna (Clarke, 2004)
(YPM 1758) (adult) radius, ulna (Chiappe, 2002)
(YPM 1759) (adult) manual phalanx I-1, phalanx II-1 (Marsh, 1880)
(YPM 1761) (>240 mm; adult) mandibular fragment (Elzanowski et al., 2001)
(YPM 1762) (adult) humerus (Clarke, 2004)
(YPM 1763) (adult) scapula, coracoid, humerus, radial fragment (Clarke, 2004)
(YPM 1764) (~269 mm; adult) partial humerus (10.5 mm wide distally), ulna (Olson, 1975)
(YPM 1765) (adult) coracoid (Chiappe, 2002)
(YPM 1766) (~240 mm; adult) coracoid (Marsh, 1880)
(YPM 1767) (adult) coracoid (Chiappe, 2002)
(YPM 1768) (adult) coracoid (Chiappe, 2002)
(YPM 1769) (adult) carpometacarpus (Clarke, 2004)
(YPM 1770) (adult) radius (Chiappe, 2002)
(YPM 1771) (adult) tarsometatarsus (Chiappe, 2002)
(YPM 1772) (adult) scapula (Chiappe, 2002)
(YPM 1773) (adult) endocast?, scapula, coracoid, humerus, radius, carpometacarpus (39.4 mm) (Chiappe, 2002)
(YPM 1774) (adult) coracoid (Clarke, 2004)
(YPM 1775) (adult) quadrates, mandible, axis, anterior dorsal vertebra, partial pygostyle(?), humerus, radius, ulna, carpometacarpus, phalanx II-1, incomplete phalanges III-1, distal femur, distal tibiotarsus (Marsh, 1880)
(YPM 1776) (adult) coracoid (Chiappe, 2002)
(YPM 6264) (<240 mm; adult) posterior mandible (Gingerich, 1972)
(YPM 9685) (~300-317 mm; adult) humerus (Clarke, 2004)
(YPM 56577) (adult) scapula, coracoid (Clarke, 2004)
Early Turonian, Late Cretaceous
Kaskapau Formation, Alberta, Canada

(UA 18456) (~220 mm) humerus (53.5 mm) (Fox, 1984)
Turonian, Cretaceous
Juan Lopez Member of Mancos Shale, New Mexico, US

(YPM 9148) (~238 mm) incomplete humerus (58 mm) (Lucas and Sullivan, 1982)
Early Coniacian, Late Cretaceous
Ector Chalk Formation of the Austin Group, Texas, US

(TMM 31051-24) (~262 mm) humerus (63.8 mm) (Parris and Echols, 1992)
(TMM 31051-25) (~257 mm) humerus (62.5 mm), partial ulna, partial radius, partial carpometacarpus (Parris and Echols, 1992)
Coniacian, Late Cretaceous
Gober Formation, Texas, US

(ET 4396) proximal carpometacarpus (Parris and Echols, 1992)
Early Campanian, Cretaceous
Mooreville Chalk, Alabama, US

(D2K coll.) material (Clarke, 2004)
(Red Mountain Museum coll.) partial skull including premaxillae and maxilla, mandible, vertebrae, pelvis, limb elements (Lamb, 1997)
(USNM 22820; holotype of Plegadornis antecessor) (~269 mm) distal humerus (10.5 mm wide distally) (Wetmore, 1962)
Campanian, Late Cretaceous
Pembina Member of the Vermillion River Formation, Manitoba, Canada

(CFDC B.80.05.14) femur (CFDC online)
Campanian, Late Cretaceous
Chico Formation, California, US

(UCMP 170785) partial humerus (Hilton et al., 1999)
Campanian, Late Cretaceous
Pflugerville Formation, Texas, US

(TMM 42522-1) (~254 mm) distal humerus (10.1 mm wide distally) (Parris and Echols, 1992)
Late Cretaceous?
US?

(USNM 11641) radius (Chiappe, 1996)
Diagnosis- (after Marsh, 1872b) cervical centra amphicoelous (also in Archaeorhynchus and Gansus).
(after Clarke, 2004) anteromedial pneumatic foramen in quadrate; proximal caudal prezygopophyses clasp dorsal surface of preceding vertebra; acromion that does not extend anteriorly past the coracoid condyle; pit-shaped fossa at distal tip of bicipital crest (also in Longicrusavis); dorsal ulnar condyle where the posterior extent of the articular surface is equal to the width of the articular surface across its distal end (unknown in other non-avian ornithuromorhs except Apsaravis); oval scar on the posteroventral surface of the distal radius in the center of the ligamentous depression; large tubercle developed on the laterodistal surface of metacarpal II; internal index process on manual phalanx II-1.
(proposed) pterygoid-quadrate articulation condylar, with a well-projected tubercle on the quadrate; splenials contacting anteriorly at symphysis; coronoid present; dorsal vertebrae with ossified connective tissue bridging transverse processes; series of short sacral vertebrae, with dorsally directed parapophyses just anterior to the acetabulum (also in Gansus and Aves); coracoid articulations on sternum cross; proximoposterior surface of deltopectoral crest concave (also in Apsaravis); well developed bicipital tubercle on ulna (also in Yixianornis and Apsaravis); V-shaped ulnare (also in Aves); postacetabular process horizontally oriented (also in Carinatae); intercotylar prominence well developed (also in derived hesperornithines and Aves);
Other diagnoses- Marsh (1872a) originally diagnosed Graculavus anceps as being larger than G. velox (which was not otherwise comparable, being based on a humerus; contra Clarke, 2004), and differing from the phalacrocoracid "Graculus violaceus" (now Phalacrocorax pelagicus) in several characters. These were- broader and flat articular surface for phalanx II-1; smaller and oval articular surface for phalanx III-1; larger distal tubercle between these surfaces. Obviously comparisons to cormorants are of little use, as Ichthyornis is not even a crown clade bird.
Marsh (1872c) distinguished Colonosaurus mudgei from mosasaurs in its lack of a conspicuous Meckelian groove, but this is common in derived birds.
Marsh (1873b) distinguished Graculavus agilis from G. anceps based on its smaller size, gracility and reduced carpal fossa. As Clarke (2004) noted, the first two differences do not seem to exist, while the third is unknown in the anceps holotype, since that only preserves the distal carpometacarpus.
Marsh (1876) distinguished Ichthyornis victor from I. dispar based on its larger size, but Clarke (2004) determined that there was a continuous variation in size of Ichthyornis specimens from the Smoky Hills Chalk and that no morphological differences between small and large specimens were apparent besides a few forelimb scars being more prominent on larger ones.
Marsh (1880) distinguished I. anceps from I. dispar based on a more slender mandible with more teeth, based on a referred specimen (YPM 1749) that cannot be compared to the anceps holotype. While Clarke (2004) thought it might be "slightly more delicate" than YPM 1450, she noted it contained the same number of teeth. Marsh distinguished I. victor from I. dispar based on the stouter and deeper mandible of YPM 1735, though Clarke notes its proportions cannot be determined as it is incomplete.
Harrison (1973) listed two humeral characters as diagnostic of Ichthyornis- dorsally projecting deltopectoral crest and small bicipital crest, but Clarke (2004) found these both to be plesiomorphic for birds.
Olson (1975) distinguished I. antecessor from supposed I. dispar specimen YPM 1764 based on several characters- more gracile humeral shaft; shallower and more distally positioned brachial fossa; ectepicondylar process more prominent; pit at base of ectepicondylar process shallower. Clarke (2004) noted the I. dispar holotype is slender as in the I. antecessor holotype and that the other differences were minor and vary in Smoky Hill Ichthyornis specimens.
Comments- While multiple species of Smoky Hill Chalk Ichthyornis were recognized early on, the lack of proper diagnoses made referral of remains to the species level uncertain through the 1900's. Elzanowski (1995), Clarke (1999, 2000), Clarke and Chiappe (2001) and Chiappe (2002) all noted the taxonomic mess and only provisionally referred elements not preserved in the holotype (or specimens which shared elements with the holotype) to the taxon, fearing multiple species were represented. Clarke (2002) examined all the specimens at the YPM for her thesis, removing some from Ichthyornis and synonymizing the others into one species, which she called Ichthyornis dispar. This study was published in 2004 in a slightly modified version that mostly differed in lacking several taxa in its phylogenetic analysis. Her taxonomy has been followed in the recent literature, though the species should be called Ichthyornis anceps as noted below.
The holotype of Ichthyornis anceps (the distal carpometacarpus YPM 1208) was discovered in 1870 and described by Marsh (1872a) as Graculavus anceps. Marsh assigned it to Graculavus because he thought it resembled phalacrocoracids, which he placed Graculavus velox near as well. Marsh (1880) later placed anceps in Ichthyornis without comment, also referring the mandible and partial humerus YPM 1749 to the species (though they are not comparable to the type). Shufeldt (1915) believed anceps was too fragmentary and distorted to diagnose or place precisely within Aves. However, Clarke (2004) noted it has Ichthyornis' apomorphic distal metacarpal tubercle and does not differ from the I. dispar holotype except in size. Clarke misinterpreted the ICZN in respect to Ichthyornis anceps vs. I. dispar when he sank the former into the latter though. Although I. anceps cannot be the type species of Ichthyornis, it can be a senior synonym of of I. dispar. Furthermore, according to the 1999 edition of the ICZN, I. anceps is not a nomen oblitum, as it was used as a valid species by Stewart (1990). To subsume I. anceps into I. dispar, it will require a formal appeal to the ICZN.
Marsh (1872b) briefly described Ichthyornis dispar as a partial bird postcranium and a week later (1872c) described Colonosaurus mudgei as reptilian mandibles similar to mosasaurs. However, these are based on the remains of one individual, as Marsh later (1873a) realized. Marsh described Ichthyornis dispar in more detail in 1873a, 1875a, 1875b and especially 1880. In the latter publication, Marsh also referred YPM 1718, 1723 and 1730 to I. dispar preseumbly based on size. Gregory (1952) believed the mandibular elements (including Colonosaurus) belonged to juvenile individuals of the mosasaur Clidastes, which was followed by several later authors. Gingerich (1972) described a posterior mandible as Ichthyornis cf. dispar, and agreed with Marsh, Russell (1967) and Walker (1967) that the toothed mandibles did belong to Ichthyornis. Olson (1975) referred YPM 1764 provisionally to I. dispar, pending a revision of Ichthyornis by Brodkorb which never appeared. Paris and Echols (1992) described a humerus and partial forelimb from the Ector Chalk Formation of Texas as I. dispar, though they are currently catalogued as I. victor in the TMM collections.
Marsh (1873b) named Graculavus agilis based on a proximal carpometacarpus (YPM 1209) found in 1872. The description was extremely brief and no type material was mentioned, though Marsh referred both Graculalvus anceps and G. agilis to the Natatores. Marsh (1880) later placed agilis in Ichthyornis without comment and referred the ulna YPM 1453 to the species (though it is not comparable to the type). Shufeldt (1915) believed the holotype was indeterminate and impossible to place precisely within Aves. Clarke (2004) found agilis was identical to other Smoky Hill Ichthyornis specimens, so synonymized it with I. dispar.
Ichthyornis victor was discovered in 1876 and described that year by Marsh as a new larger species of Ichthyornis. This was based on YPM 1452, which consists of three partial forelimb elements. Marsh (1880) described and referred numerous specimens to I. victor- YPM 1447, 1456, 1457, 1458, 1461, 1463, 1464, 1724, 1726, 1727, 1732, 1733, 1735, 1739, 1741, 1742, 1743, 1745 and 1775. While a partial coracoid was originally associated with YPM 1459, Clarke (2004) noted it articulates perfectly with a partial coracoid from YPM 1458, so was moved to that specimen. Hope (2002) illustrates these specimens as Ichthyornis sp., with the old coracoid number. Chinsamy et al. (1998) described the histology of KUVP 2294, a specimen they referred to I. victor. Clarke (1999) considered I. victor a chimera, because the mounted skeleton which was incorrectly labeled as the holotype actually contained elements from several Ichthyornis specimens (YPM 1447, 1453, 1461, 1724, 1728, 1732, 1733, 1739, 1741) as well as what would become the holotype of Iaceornis (which was previously noticed by Howard, 1955 and Elzanowski, 1995). Clarke (2004) noted YPM 1732 differs from the I. dispar holotype in having twelve sacral vertebrae, though the victor holotype is identical to dispar except in size. If the species really are distinct and diagnosed partially by size, I. anceps would be the valid name for the large species (with agilis, victor and validus as synonyms) while I. dispar would be the valid name for the small species.
Ichthyornis validus based on an ulna (YPM 1740) discovered in 1877 and not diagnosed by Marsh when he named it in 1880. Brodkorb (1967) claimed a radius was also known for YPM 1740, but this seems to be untrue. The partial coracoid YPM 1446 was referred to validus by Marsh (1880) without comment. Clarke (2004) noted it was more robust and larger than most other YPM specimens, the supracoracoid foramen did not lie in a groove, and that there is a unique groove extending from the supracoracoid foramen in the triossial canal. The holotype is the only subadult YPM specimen of Ichthyornis known, and is larger than some adult specimens such as the dispar holotype. Clarke synonymized it with I. dispar since it is morphologically identical.
Wetmore (1962) described a distal humerus (USNM 22820) as Plegadornis antecessor, which he thought was a ciconiiform close to threskiornithids. Kashin (1972) noted that Plegadornis was preoccupied by a genus named by Brehm in 1855, which in turn is a junior synonym of the threskiornithid genus Plegadis. Thus he renamed the genus Angelinornis. Olson (1975) synonymized Angelinornis with Ichthyornis but retained Ichthyornis antecessor as a valid species. Paris and Echols (1992) described a distal humerus (TMM 42522-1) from the Pflugerville Formation of Texas and proximal carpometacarpus (ET 4396) from the Gober Formation of Texas and referred them to Ichthyornis antecessor. The humerus was referred because it was thought to live at a later time than Smoky Hill Ichthyornis and compare better morphologically to the antecessor holotype, but the former is not necessarily true while Clarke notes it is equally similar to the I. dispar holotype. It is currently catalogued as I. sp. in the TMM collections. The carpometacarpus was only tentatively referred based on stratigraphy and supposed differences from Smoky Hill Ichthyornis material, but Clarke could not confirm these differences. As noted above, Clarke determined the supposedly distinct characters of antecessor fell within the range of individual variation for Smoky Hill Chalk Ichthyornis, so synonymized this species with I. dispar.
Martin and Stewart (1977) described the jaws of a skeleton found in 1970, which was found in 1970 and referred to Ichthyornis sp.. While they referred to this specimen as SMM 13520, though it is actually 2503. Clarke (2004) referred this specimen to I. dispar.
Lucas and Sullivan (1982) described a humerus (YPM 9148) from the Mancos Shale in New Mexico found in 1979 as Ichthyornis sp., but Clarke (2004) referred it to I. dispar.
References- Marsh, 1872a. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3, 359-365.
Marsh, 1872b. Notice of a new and remarkable fossil bird. American Journal of Science, 3rd series. 4, 344.
Marsh, 1872c. Notice of a new reptile from the Cretaceous. American Journal of Science, 3rd series. 4(23), 406.
Marsh, 1873a. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Marsh, 1873b. Fossil birds from the Cretaceous of North America. American Journal of Science, 3rd series. 5, 229-230.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Marsh, 1876. Notice of new Odontornithes. American Journal of Science, 3rd series. 11, 509-511.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Marsh, 1883. Birds with teeth. 3rd Annual Report of the Secretary of the Interior. 3, 43-88.
Shufeldt, 1893. Comparative osteological notes on the extinct bird Ichthyornis. Journal of Anatomy and Physiology. 27(3), 336-342.
Williston, 1898. Birds. The University Geological Survey of Kansas, Part 2. 4, 43-53.
Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Edinger, 1951. The brains of the Odontognathae. Evolution. 5(1), 6-24.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Howard, 1955. A new wading bird from the Eocene of Patagonia. American Museum Novitates. 1710, 25 pp.
Wetmore, 1962. Notes on fossil and subfossil birds. Smithsonian Miscellaneous Collections. 145, 1-17.
Brodkorb, 1967. Catalogue of fossil birds: part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). Bulletin of the Florida State Museum (Biological Sciences). 11, 99-220.
Russell, 1967. Systematics and morphology of American mosasaurs. Peabody Museum of Natural History, Yale University Bulletin. 23, 1-240.
Walker, 1967. Revival of interest in the toothed birds of Kansas. Kansas Academy of Science, Transactions. 70(1), 60-66.
Gingerich, 1972. A new partial mandible of Ichthyornis. Condor. 74, 471-473.
Kashin, 1972. New name for the genus Plegadornis. Ornitologiya. 10, 336-337.
Harrison, 1973. The humerus of Ichthyornis as a taxonomically isolated character. Bulletin of the British Ornithological Club. 93, 123-126.
Harrison and Walker, 1973. Wyleyia: A new bird humerus from the Lower Cretaceous of England. Palaeontology. 16(4), 721-728.
Olson, 1975. Ichthyornis in the Cretaceous of Alabama. Wilson Bulletin. 87, 103-105.
Martin and Stewart, 1977. Teeth in Ichthyornis (Class: Aves). Nature. 195, 1331-1332.
Lucas and Sullivan, 1982. Ichthyornis in the Late Cretaceous Mancos shale (Juan Lopez member), northwestern New Mexico. Journal of Paleontology. 56, 545-547.
Fox, 1984. Ichthyornis (Aves) from the early Turonian (Late Cretaceous) of Alberta. Canadian Journal of Earth Sciences. 21, 258-260.
Stewart, 1988. A new specimen of Ichthyornis, and its implications for interpreting relationships of the group. Second International Symposium of the Society of Avian Paleontology and Evolution.
Stewart, 1990. Niobrara Formation vertebrate stratigraphy. In Bennett (ed). Niobrara Chalk excursion guidebook. Lawrence: University of Kansas Museum of Natural History. 19-30.
Parris and Echols, 1992. The fossil bird Ichthyornis in the Cretaceous of Texas. Texas Journal of Science. 44, 201-212.
Elzanowski, 1995. Cretaceous birds and avian phylogeny. Courier Forschungsinstitut Senckenberg. 181, 37-53.
Chiappe, 1996. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Lamb, 1997. Marsh was right: Ichthyornis had a beak! Journal of Vertebrate Paleontology. 17(3), 59A.
Chinsamy, Martin and Dodson, 1998. Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas. Cretaceous Research. 19(2), 225-233.
Clarke, 1999. New information on the type material of Ichthyornis: Of chimeras, characters and current limits of phylogenetic inference. Journal of Vertebrate Paleontology. 19(3), 38A.
Hilton, Gohre, Embree and Stidham, 1999. California's first fossil evidence of Cretaceous winged vertebrates. California Geology. 52(4), 4-10.
Clarke, 2000. Ichthyornis and Apatornis reappraised. 5th International Meeting of the Society of Avian Paleontology and Evolution and the Symposium on Jehol Biota. Vertebrata PalAsiatica. 38(suppl.), 9.
Clarke and Chiappe, 2001. A new carinate bird from the Late Cretaceous of Patagonia (Argentina). American Museum Novitates. 3323, 1-23.
Elzanowski, Paul and Stidham, 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology. 20(4), 712-719.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Clarke, 2003. The morphology, taxonomy and systematic position of Ichthyornis; A case study of alpha taxonomic practice in a phylogenetic frame. Journal of Vertebrate Paleontology. 23(3), 41A.
Everhart, online 2003-2007. http://www.oceansofkansas.com/Ichthyornis.html
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Burnham and Hines, 2005. Transfer preparation of an Ichthyornis specimen from the Niobrara Formation. Journal of Vertebrate Paleontology. 25(3), 41A.
I. sp. (Walker, 1967)
Early Turonian, Late Cretaceous
Pfeifer Shale Member of the Greenhorn Limestone or Fairport Chalk Member of the Carlile Shale, Kansas, US

Material- (FHSM VP-2139; = FSHM 11285; = SMM 2139) (~240 mm) proximal carpometacarpus
Comments- Walker (1967) first noted this specimen as "“a fragmentary wing element of Ichthyornis", and it was later called FSHM 11285 by Martin and Stewart (1982). Clarke (2002, 2004) referred the carpometacarpus to Ichthyornis based on morphological similarity, and Shimada and Fernandes (2006) described and illustrated the specimen as Ichthyornis sp..
References- Walker, 1967. Revival of interest in the toothed birds of Kansas. Kansas Academy of Science, Transactions. 70(1), 60-66.
Martin and Stewart, 1982. An ichthyornithiform bird from the Campanian of Canada. Canadian Journal of Earth Sciences. 19, 324-327.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Fernandes and Shimada, 2005. A Turonian (Late Cretaceous) bird bone from Kansas. 6th Annual Kansas Academy of Science Paleontology Symposium, Abstracts.
Shimada and Fernandes, 2006. Ichthyornis sp. (Aves: Ichthyornithiformes) from the lower Turonian (Upper Cretaceous) of western Kansas. Transactions of the Kansas Academy of Science. 109(1/2), 21-26.
I? sp. (Zinsmeister, 1985)
Late Cretaceous
Seymour Island, Antarctica

Reference- Zinsmeister, 1985. 1985 Seymour Island expedition. Antarctic Journal of U.S. 20, 41-42.
I? sp. (Cumbaa and Tokaryk, 1993)
Middle Cenomanian, Late Cretaceous
Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada

Material- (SMNH P2077.11) partial coracoid (Tokaryk et al., 1997)
(SMNH P2077.67) partial coracoid (Tokaryk et al., 1997)
(SMNH P2077.71) radius (Tokaryk et al., 1997)
(SMNH P2077.111) partial coracoid (Tokaryk et al., 1997)
(SMNH P2077.112) partial coracoid (Tokaryk et al., 1997)
(SMNH P2487.5) partial coracoid (Tokaryk et al., 1997)
elements including humerus (Cumbaa et al., 2006)
Comments- Cumbaa and Tokaryk (1993) mentioned two ichthyornithids from the Ashville Formation of Saskatchewan, which were later described by Tokaryk et al. (1997) as Ichthyornis species A (SMNH P2077.11, P2077.67, P2077.112 and P2487.5), Ichthyornis species B (SMNH P2077.111) and I. sp. indet. (SMNH P2077.71). They referred the specimens to Ichthyornis based on the coracoid scapular facet being nearly parallel to the sternal end of the glenoid facet, which Clarke (2004) noted was found in Ichthyornis, but not apomorphic. Tokaryk et al. distinguished species A from species B by its gracility and round (vs. angular) scapular facet. Longrich (2009) suggested the Ashville coracoids did not resemble Ichthyornis, and were referrable to Pasquiaornis based on their dimorphism (P. hardiei vs. P? tankei), pachyostosis, and supposed lack of coracoids in the Pasquiaornis material. However, Tokaryk et al. (1997) did identify one partial coracoid as Pasquiaornis (SMNH P2077.113), though this was not described nor illustrated. Also, Cumbaa et al. (2006) mention Ichthyornis-like bones and another Pasquiaornis coracoid from the Bainbridge River bed of the same member, but these are still under study. Study of the Bainbridge River material and SMNH P2077.71 should clarify matters.
References- Cumbaa and Tokaryk, 1993. Early birds, crocodile tears, and fish tales: Cenomanian and Turonian marine vertebrates from Saskatchewan, Canada. Journal of Vertebrate Paleontology. 13(3), 31A-32A.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
I? sp.
Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Material
- (AMNH 110) sacrum (AMNH online)
I? sp.
Late Cretaceous?
US
Material
- (AMNH 985) proximal scapula, proximal humerus (AMNH online)

Ornithurae sensu Chiappe, 1991
Definition- (Hesperornis regalis + Passer domesticus) (modified)
Diagnosis- at most a small dorsal projection of the maxilla participates in the anterior margin of the antorbital fenestra (unknown in other ornithuromorphs); ectopterygoid absent (unknown in other euornithines sensu Sereno); pubic boot absent (unknown in Ichthyornis; also in Hongshanornis and Patagopteryx); obturator flange on ischium (unknown in Ichthyornis; also in Patagopteryx and Chaoyangia).

Hesperornithes Furbringer, 1888
Definition- (Hesperornis regalis <- Passer domesticus) (Sereno, in press; modified from Clarke, 2004)
= Odontolcae Marsh, 1875a
Definition- (Teeth set in grooves as in Hesperornis regalis) (Martyniuk, 2012)
= Odontognathes Marsh, 1880
= Dromaeopappi Stejneger, 1885
= Odontoholcae Stejneger, 1885
= Enaliornithes Furbringer, 1888
= Hesperornithomorphi Hay, 1930
Diagnosis- (after Marsh, 1875) all presacral vertebrae heterocoelous (also in Aves).
(proposed) quadrate not pneumatic; metatarsals III and IV do not distally enclose vascular foramen (also in non-ornithothoracines; absent in Hesperornis).
Other diagnoses- Marsh (1875a, b) diagnosed his new taxon Odontolcae based on several characters. Teeth set in grooves are found in Hesperornis and Parahesperornis (and in adult Ichthyornis), but are unknown in more basal hesperornithines. The keeless sternum is present in Hesperornis and probably Baptornis but still unknown for more basal genera, while the reduced forelimb is present at least as early as Pasquiaornis, but unknown in Enaliornis.
Comments- Marsh (1875a) named Odontolcae as an order including Hesperornis but not Ichthyornis. Martyniuk (2012) gave it an apomorphy-based definition, which due to Ichthyornis actually possessing dentary teeth placed in a groove, and the uncertain relationship between Ichthyornis, Hesperornis and Aves (which lack teeth), cannot be applied to any node with certainty given current information. Stejneger (1885) modified it to be the subclass Odontoholcae, and named the order Dromaeopappi.
Romer (1933) placed Eupterornis from the Paleocene of France in Baptornithidae, but is was reassigned to Gaviiformes by Brodkorb (1963). Brodkorb (1963) placed Neogaeornis in in Baptornithidae, but it was placed in Gaviiformes by Olson (1992). Nessov (1992) had identified KKM KP 4925/P131 as the incomplete humerus of a hesperornithine, but later (in Mourer-Chauvire, 1992) determined it was a mosasaur limb element. Longrich (2006) stated the dorsal vertebra RTMP 89.81.12 from the Dinosaur Park Formation of Alberta was a possible hesperornithine, but later (2009) referred it to Palintropus sp.. Dyke et al. (2011) referred a supposed distal femur (MTCO 17637) from the Cornet bauxite of Romania to Hesperornithes, but Agnolin and Varricchio (2012) believe it is more similar to an azhdarchid proximal radius.
References- Marsh, 1872. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3, 359-365.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Stejneger, 1885. Birds. in Kingsley (ed). The Standard Natural History. Volume 4.
Furbringer, 1888. Untersuchungeb zur Morphologie und Systematik der Vogel. Amsterdam: Holkema. 1751 pp.
Shufeldt, 1890. On the affinities of Hesperornis. Nature. 43, 176.
Thompson, 1890. On the systematic position of Hesperornis. Studies from the Museum of Zoology. 1(10), 15 pp.
Anonymous, 1891. Professor Thompson on the systematic position of Hesperornis. Auk. 8(3), 304-305.
Helm, 1891. On the affinities of Hesperornis. Nature. 43, 368.
Marsh, 1897. The affinities of Hesperornis. Nature. 55, 534.
Hay, 1930. Second bibliography and catalogue of the fossil vertebrata of North America, Volume 2. Carnegie Institution of Washington Publication, 390, 1074 pp.
Romer, 1933. Vertebrate Paleontology. University of Chicago Press, Chicago.
Brodkorb, 1963. Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bull. Florida State Mus., Bioi. Sci.. 7, 179-293.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Olson, 1992. Neogaeornis wetzeli Lambrecht, a Cretaceous loon from Chile (Aves: Gaviidae). Journal of Vertebrate Paleontology. 12, 122-124.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Longrich, 2006. An ornithurine bird from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 43(1), 1-7.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Dyke, Benton, Posmosanu and Naish, 2011. Early Cretaceous (Berriasian) birds and pterosaurs from the Cornet bauxite mine, Romania. Palaeontology. 54(1), 79-95.
Agnolin and Varricchio, 2012 . Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird. Geodiversitas. 34(4), 883-894.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Hesperornithformes Sharpe, 1899
Definition- (Hesperornis regalis + Enaliornis barretti) (Martyniuk, 2012)
References- Sharpe, 1899. A hand-list of the genera and species of birds. Vol. I. London. British Museum (Natural History).
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Potamornis Elzanowski, Paul and Stidham, 2001
P. skutchi Elzanowski, Paul and Stidham, 2001
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Holotype
- (UCMP 73103) quadrate (18 mm)
Referred- ?(University of Nebraska coll.) tarsometatarsus (Elzanowski, Paul and Stidham, 2001)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US

Referred- ?(UCMP 117605) tarsometatarsus (Elzanowski, Paul and Stidham, 2001)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US

Referred- ?(UCMP 159207) distal tarsometatarsus (UCMP online)
?(UCMP 159208) femur (UCMP online)
?(UCMP 174715) tibiotarsus (UCMP online)
?(UCMP 174718) dorsal vertebra (UCMP online)
?(UCMP 187203) tarsometatarsus (UCMP online)
?(UCMP 187205) vertebra (UCMP online)
?(UCMP 187206) vertebra(UCMP online)
Diagnosis- (after Elzanowski et al., 2001) distinct medial depression for m. protractor pterygoidei et quadrati dorsal to orbital process.
Other diagnoses- Elzanowski et al. (2001) list the strongly asymmetrical quadrate head, with the beak-shaped medial part overhanging the otic process as an apomorphy, but note it is also present in most palaeognaths, Psophia, Cariama and Opisthocomus. Similarly, they list the presence of a quadratojugal buttress as diagnostic, but then state it is also present in Baptornis and Parahesperornis. A pit on the medial part of the quadrate head and small orbital process are also present in Ichthyornis, so are possibly plesiomorphies. Elzanowski et al. state the low angle between the lateral and medial condyles is diagnostic, as those of Baptornis and hesperornithids are higher, but that of Ichthyornis is even lower, making it a probable plesiomorphy. The smooth connection between medial and "posterior" condyles is plesiomorphic (Clarke, 2004), while contra Elzanowski et al., the lateral condyle is separated from the posterior articular surface by a groove.
Comments- Elzanowski et al. (2001) do not describe the tentatively referred paratype tarsometatarsi, merely stating they are the right size to belong to Potamornis. The UCMP specimens are identified as Potamornis in the UCMP collections, but cannot be compared to the holotype. UCMP 159208, 187205 and 187206 are from the Danian (Paleocene), so were presumably reworked. While the lack of pneumaticity and quadratojugal buttress suggests Potamornis is a hesperornithine, the lack of and elongate orbital process excludes it from the Parahesperornis + Hesperornis clade. Further resolution is difficult as so few hesperornithine quadrates are known and no postcranial material referred to Potamornis is described.
References- Elzanowski, Paul and Stidham, 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology. 20(4), 712-719.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.

unnamed Hesperornithes (Kurochkin, 1988)
Late Campanian-Early Maastrichtian, Late Cretaceous
Nemegt Formation, Mongolia

Material- (IGM 100/1311) distal tibiotarsus (12.1 mm wide) (Clarke and Norell, 2004)
distal tibiotarsus (11.7 mm wide) (Kurochkin, 1988)
? partial mandible, cervical vertebra (Kurochkin, 2000)
Comments- Kurochkin (1988) identified a specimen as Baptornis sp., and later (2000) as closer to Parahesperornis. Clarke and Norell (2004) described a similar specimen and referred both to nonavian ornithurines (sensu Gauthier and de Queiroz), though they did note characters were shared with Baptornis while Kurochkin's Parahesperornis-like characters were disputed. They were skeptical of referring isolated Cretaceous diving ornithuromorph specimens to Hesperornithines, though no reasons were given for removing any of it from that clade, and it seems most parsimonious to assume a single clade of Mesozoic taxa with hesperornithine-like limbs until shown otherwise. The elements are more similar to Enaliornis? seeleyi than Baptornis in the anteriorly rounded lateral condyle in distal view, though the anterior intercondylar sulcus is narrower as in Baptornis. The medial projection of the medial condyle is intermediate between the two taxa, while the extensor groove extends less distally than in both.
Kurochkin (2000) mentioned a small mandible and cervical vertebra which were "somewhat different" from other hesperornithines. He referred these to "Hesperornithiformes fam. nov." along with the then unnamed holotype of Brodavis mongoliensis though he did not list any diagnostic characters.
References- Kurochkin, 1988. [Cretaceous birds of Mongolia and their significance for study of the phylogeny of class Aves.] Trudy Sovmestnoi Sovetsko-Mongolskoi Paleontologicheskoi Ekspeditsii. 34, 33-42.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Clarke and Norell, 2004. New avialan remains and a review of the known avifauna from the Late Cretaceous Nemegt Formation of Mongolia. American Museum Novitates. 3447. 12 pp.

undescribed hesperornithine (Mourer-Chauvire, 1991)
Maastrichtian, Late Cretaceous
Zhuravlovskaya Svita (not Eginsaiskaya Svita), Kazakhstan

Material- (PO coll.) tibiotarsal shaft, distal tibiotarsi (Nessov in Chauvire-Mourer, 1991)
Comments- Nessov (in Mourer-Chauvire, 1991) first mentioned two hesperornithine tibiotarsi from this locality, which may be this material. Nessov (in Mourer-Chavire, 1992) mentioned small hesperornithine material slightly larger than Baptornis advenus and referred to Baptornithidae, but not Baptornis itself because "of the peculiar structure of the fossa on the tibiotarsus, related to the side of the foramen interosseum proximale, and because the crista fibularis is not so strongly turned behind as in Baptornis, and much weaker." Nessov and Yarkov (1993) reported these as Baptornithidae indet., and Nessov (1997) commented on small hesperornithine material, some of which he thought was possibly referrable to Baptornis. Panteleev et al. (2004) thought this was possibly based on juvenile specimens of Asiahesperornis, while Dyke et al. (2006) thought it "probably pertains to a smaller hesperornithiform taxon, an area for future work." As the traditional Baptornithidae is paraphyletic and there is no evidence the Zhuravlovskaya tibiotarsi are more closely related to Baptornis than to Hesperornis, they are here placed as Hesperornithes incertae sedis.
References- Mourer-Chauvire, 1991. Society of Avian Paleontology and Evolution Information Newsletter. 5.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Nessov, 1997. Cretaceous non-marine vertebrates of Northern Eurasia. St. Petersburg State University, St-Petersburg. 218 pp.
Panteleev, Popov and Averianov, 2004. New record of Hesperornis rossicus (Aves, Hesperornithiformes) in the Campanian of Saratov Province, Russia. Paleontological Research. 8(2), 115-122.
Dyke, Malakhov and Chiappe, 2006. A re-analysis of the marine bird Asiahesperornis from northern Kazakhstan. Cretaceous Research. 27(6), 947-953.

undescribed Hesperornithes (Mourer-Chauvire, 1992)
Early Cretaceous
Antarctica
Comments
- Mourer-Chauvire (1992) reported that Hou would be studying hesperornithiformes from the Antarctic, though these have yet to be described.
Reference- Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.

undescribed Hesperornithes (Kirkland et al., 1997)
Late Albian, Early Cretaceous
Mussentuchit Member of the Cedar Mountain Formation, Utah, US

Material- many teeth
Comments- Kirkland et al. (1997) listed Hesperornithiformes indet., while Cifelli et al. (1999) noted two Avialae dental morphs, one referrable to Hesperornithiformes. They described the latter specimens as having bulbous bases and rare serrations.
References- Kirkland, Britt, Burge, Carpenter, Cifelli, DeCourten, Eaton, Hasiotis and Lawton, 1997. Lower to Middle Cretaceous dinosaur faunas of the Central Colorado Plateau: a key to understanding 35 million years of tectonics, sedimentology, evolution, and biogeography. Brigham Young University Geology Studies. 42, 69-103.
Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen, 1999. Medial Cretaceous vertebrates from the Cedar Mountain Formation, Emery County, Utah: the Mussentuchit Local Fauna. in Gillette (ed.). Vertebrate Paleontology in Utah. Utah Geological Survey, Miscellaneous Publication. 99-1, 219-242.

undescribed hesperornithine (Sanchez, Cumbaa and Schroder-Adams, 2009)
Middle Cenomanian, Late Cretaceous
Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada

Comments- Sanchez note that among the 250 bird bones from the Bainbridge River Bonebed (most of which are Pasquiaornis), some are from a "possible new hesperornithiform genus."
Reference- Sanchez, Cumbaa and Schroder-Adams, 2009. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Journal of Vertebrate Paleontology. 29(3), 175A.

undescribed hesperornithine (Tanaka, Kobayashi, Kano and Kurihara, 2012)
Early Santonian, Late Cretaceous
Kashima Formation of the Yezo Group, Japan
Material
- three cervical vertebrae, three dorsal vertebrae, distal femora, partial fibula
Reference- Tanaka, Kobayashi, Kano and Kurihara, 2012. The first record of a hesperornithiform from Japan. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 183.

Enaliornithidae Furbringer, 1888
Definition- (Enaliornis barretti <- Hesperornis regalis) (Martyniuk, 2012)
References- Furbringer, 1888. Untersuchungen zur Morphologie und Systematik der Vogel, zugleich ein Beitrag zur Anatomie der Stutz- und Bewegungsorgane. Verlag von T.J. van Holkema, Amsterdam. 1751 pp.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Enaliornis Seeley, 1876
= "Pelargonis" Seeley, 1864
= "Palaeocolyntus" Seeley, 1864
= "Pelagornis" Seeley, 1866 (preoccupied Lartet, 1857)
= "Enaliornis" Seeley, 1869
= "Palaeocolymbus" Seeley, 1876
Diagnosis- (after Galton and Martin, 2002b) posteromedial ridge on distal portion of metatarsal II (unknown in Pasquiaornis; also in Hesperornis? mengeli).
Other diagnoses- Galton and Martin (2002a) cited additional characters. The moderately sized antitrochanter is unlike Baptornis advenus and Hesperornis, but is symplesiomorphic as "Baptornis" varneri and Ichthyornis are comparable. The lack of a femoral neck is caused by a lack of marked ventral concavity below the head in some specimens (e.g. SMC B55287, B55289) and the lack of a a proximal concavity between the trochanteric crest and head in other specimens (SMC 55290, BMNH A483). Thus it is not homologous, and it varies within species as well. The medial tarsometatarsal cotyla is reduced in all hesperornithines. The tarsometatarsus is distally arched in all hesperornithines. Having the trochlea of metatarsals III and IV subequal in size is plesiomorphic for hesperornithines, also found in Pasquiaornis, Baptornis and "B." varneri. The trochlea of metatarsal IV does not extend dorsally past that of III, which is unlike Pasquiaornis? tankei , Baptornis, Parahesperornis and Hesperornis but also plesiomorphically found in most other theropods such as Gansus.
Galton and Martin (2002b) also included the ventrally keeled anterior synsacrum in their diagnosis, but this is only known for certain in E. barretti. The hypotarsal ridge on metatarsal III is also present in some Hesperornis species (e.g. H. regalis and H. chowi).
Comments- The first Enaliornis specimens may be bird bones found in 1858 and noted by Lyell (1859), and a hesperornithiform distal tarsometatarsus mentioned by Owen (1861). None of this material was in the Woodwardian Museum (now part of the SMC) when Seeley examined it in 1859 though (Seeley, 1866). Seeley (1864) mentioned two new bird taxa in the title of an article ("Pelargonis sedgwicki" and "Palaeocolyntus barretti"), but as nothing else was published, these are nomina nuda. He later (1866) mentioned the name "Pelagornis barretti" (note the genus was spelled correctly this time) in a summary paragraph, which was also a nomen nudum. Because Pelagornis was preoccupied by a pelagornithid "odontopterygiform" genus, Seeley (1869) placed his two species in the new genus "Enaliornis." However, these names are only used in a list of taxa which references a list of bones at the Woodwardian Museum (now at the SMC), with no element referred to any particular species. This makes them nomina nuda, as does Seeley's statement that names used in the paper are not meant to take taxonomic precedence. While Seeley does type "J. d, p.7" after E. barretti and "p. 8" after E. sedgwicki, the specimens are listed in order of tablet in their drawer, and those few on page 8 (tablets 18-20) don't seem to be purposefully separated from those on page 7 (tablets 1-17). Seeley (1876) finally described his two species officially, also noting the prior use of "Palaeocolyntus" was a misspelling of "Palaeocolymbus." However, he did not designate holotypes for each species and left many specimens unfigured and referred to in passing, often not assigned to a particular species. Elzanowski and Galton (1991) redescribed the braincases, while Galton and Martin (2002a, b) redescribed the postcrania. The latter two references also excluded a number of remains from Enaliornis, and Galton and Martin (2002b) revised the taxonomy of the genus, assigning most elements to particular species and erecting the new species E. seeleyi.
YORYMG 584 was identified as an Enaliornis dorsal vertebra by Seeley (1876), but is a posterior cervical vertebra of a non-hesperornithine bird (Galton and Martin, 2002a, b). SMC B55286 is a caudal vertebra identified as "Enaliornis" by Seeley (1869) and Enaliornis by Seeley (1876), but was reidentified as the testudine Rhinochelys by Galton and Martin (2002b). SMC B55328 was stated to be a proximal coracoid by Seeley (1869), and while possibly true, Galton and Martin (2002b) and Galton et al. (2009) exclude it from Hesperornithes. This will be redescribed by Galton (in prep.). One "Enaliornis" sacrum was mentioned in the Woodwardian Museum by Seeley (1869), but it is uncertain which of SMC B55281-55284 it was.
References- Lyell, 1859. Manual of Elementary Geology, Supplement to the 5th Edn. 3rd Edn. Murray, London. 40 pp.
Owen, 1861. Palaeontology, 2nd Edn. A. & C. Black, Edinburgh. xvi + 463 pp.
Seeley, 1864. On the fossil birds of the Upper Greensand, Palaeocolyntus barretti and Pelargonis sedgwicki. Proc. Cambridge Phil. Soc. 1, 228.
Seeley, 1866. Note on some new genera of fossil birds in the Woodwardian Museum. Ann. Mag. Nat. Hist. (3). 18, 109-110.
Seeley, 1869. Index to the fossil remains of Aves, Ornithosauria and Reptilia, from the Secondary System of strata arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell & Co.,
Cambridge. 143 pp.
Seeley, 1876. On the British fossil Cretaceous birds. Quarterly Journal of the Geological Society of London. 32, 496-515.
Elzanowski and Galton, 1991. Braincase of Enaliornis, an Early Cretaceous bird from England. Journal of Vertebrate Paleontology. 11(1), 90-107.
Galton and Martin, 2002a. Enaliornis, an Early Cretaceous hesperornithiform bird from England, with comments on other Hesperornithiformes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 317-338.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
Galton and Martin, 2003. Enaliornis Seeley, 1876, the earliest foot-propelled diving bird (Aves, Ornithurae, Hesperornithiformes, Enaliornithidae), and other bird bones from the Cambridge Greensand (Early Cretaceous, Albian, ~100 MA) near Cambridge, southern England. Journal of Vertebrate Paleontology. 23(3), 53A.
Galton, Dyke and Kurochkin, 2009. Re-analysis of Lower Cretaceous fossil birds from the UK reveals an unexpected diversity. Journal of Vertebrate Paleontology. 29(3), 102A.
Galton, in prep. Additional bird bones (Hesperornithiformes Enaliornis and Aves incertae sedis) from the Early Cretaceous of England. Revue Paleobiologie.
E. barretti Seeley, 1876
= "Palaeocolyntus barretti" Seeley, 1864
= "Pelagornis barretti" Seeley, 1866
= "Enaliornis barretti" Seeley, 1869
= "Palaeocolymbus barretti" Seeley, 1876
Late Albian, Early Cretaceous
Cambridge Greensand, England
Lectotype
- (BMNH A477) (adult) distal tarsometatarsus
Paralectotypes- (BGS 87932) (juvenile) proximal metatarsus (11.7 mm)
?(BGS 87936) (juvenile) partial ilium, proximal pubis, proximal ischium
?(SMC B54404) (adult) braincase (Seeley, 1869)
?(SMC B55277) (adult) posteriormost dorsal vertebra (11.1 mm) (Seeley, 1869)
?(SMC B55282) (adult) anterior synsacrum
(SMC B55312) (juvenile) proximal tibiotarsus (Seeley, 1869)
(SMC B55313) (adult) proximal tibiotarsus (Seeley, 1869)
(SMC B55316) (juvenile) distal tibiotarsus (15.2 mm wide) (Seeley, 1869)
?(YORYMG 507) thirteenth or fourteenth cervical vertebra (11.6 mm)
Referred- (BMNH A163) (adult) distal femur (21.3 mm wide) (Lydekker, 1891)
(BMNH A483; = BMNH A483a) (juvenile) proximal femur (Galton and Martin, 2002a)
(BMNH A5803; = BMNH A483b) (adult) proximal femur (Galton and Martin, 2002a)
?(SMC B55284) (adult) posterior synsacrum (Seeley, 1876)
(SMC B55303) (adult) distal femur (~20.5 mm wide)
(SMC B55304) (adult) distal femur (Seeley, 1869)
(SMC B55305) (adult) distal femur (Seeley, 1869)
(SMC B55306) (adult) distal femur (Seeley, 1869)
(SMC B55322) (adult) distal tibiotarsus (Galton and Martin, 2002b)
(SMC B55331) (adult) proximal tarsometatarsus (12.5 mm wide) (Galton and Martin, 2002a)
(YORYMG 587) (adult) proximal tibiotarsus (Galton and Martin, 2002a)
(YORYMG 591) (adult) distal femur (Galton and Martin, 2002b)
Diagnosis- (after Seeley, 1976) larger than E. sedgwicki and E. seeleyi.
(after Galton and Martin, 2002b) slope of lateral condyle continuous with intercondylar sulcus that meets the medial condyle at an obtuse angle.
(proposed) centra of anterior synsacral centra transversely constricted ventrally to form a median longitudinal ridge; anterior projection of medial tibiotarsal condyle much wider than deep.
Other diagnoses- Galton and Martin (2002b) proposed several additional diagnostic characters. The large and rugose trochanteric crest in adult specimen BMNH A5803 (cited as diagnostic by Galton and Martin, 2002b) is also present in Hesperornis, ontogenetically variable and is unknown in E? seeleyi. The cnemial crest is no taller than in E? sedgwicki and is actually less laterally flared compared to the lateral extent of the proximal tibial articular surface. The increased depth of the tibiotarsal condyles (minimum depth over half of transverse width) may be plesiomorphic, as it is also present in Gansus. The tibiotarsal condyles are even more massive anteriorly in Hesperornis, while the medial condyle is massive in E? seeleyi. The laterally positioned posterior intercondylar sulcus on the tibiotarsus is also present in E? sedgwicki. Small, angular posterior tibiotarsal condyles are also present in other Enaliornis species and in Baptornis. The medial cotyla is not transversely compressed in Ichthyornis, Parahesperornis, Hesperornis bairdi and H. mengeli.
Comments- Brodkorb (1963) made E. barretti the type species of Enaliornis and designated BMNH A112 (mistyped A1112) the lectotype, which is a cast of BMNH A477. Seeley originally catalogued (1869) and described (1870a, b) the braincase SMC B54404 as a pterosaur. The partial pelvis BGS 87936 is misidentified as 87431 in the text and 87436 in figure 1 of Galton and Martin (2002b). SMC B55277 and B55304-55306 were identified as "Enaliornis" by Seeley (1869). While the referred femora were no doubt among the many noted to exist by Seeley (24 femora from the Woodwardian Museum now at the SMC; 6 femora from the Jesson collection now at the BMNH), they were not identified to species in that work. SMC B55312 and 55313 were listed as "Enaliornis" by Seeley (1869). SMC B55313 is no doubt one of the four large proximal tibiotarsi referred to E. barretti by Seeley (1876) (the others being SMC B55312, BMNH A478, YOYRMG 587/8), so should be a paralectotype, contra Galton and Martin (2002b). SMC B55316 is probably one of the two distal tibiae listed as "Enaliornis" by Seeley (1869). Proximal metatarsus SMC B87932 is misidentified as B17432 by Galton and Martin (2002b) in the section on proximal tarsmetatarsal variation.
SMC B55281 was identified by Seeley (1876) as a partial sacrum of E. barretti, reidentified as a pterosaur notarium by Galton and Martin (2002a), then identified again as a possible theropod sacrum by Galton and Martin (2002b). SMC B55285 is a caudal vertebra identified as "Enaliornis" by Seeley (1869) and E. barretti by Seeley (1876) but was reidentified as Chelonia indet. by Galton and Martin (2002a) and specified as Rhinochelys by Galton and Martin (2002b).
References- Seeley, 1864. On the fossil birds of the Upper Greensand, Palaeocolyntus barretti and Pelargonis sedgwicki. Proc. Cambridge Phil. Soc. 1, 228.
Seeley, 1866. Note on some new genera of fossil birds in the Woodwardian Museum. Ann. Mag. Nat. Hist. (3). 18, 109-110.
Seeley, 1869. Index to the fossil remains of Aves, Ornithosauria and Reptilia, from the Secondary System of strata arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell & Co.,
Cambridge. 143 pp.
Seeley, 1870a. The Omithosauria: an Elementary Study of the Bones of Pterodactyles, made from Fossil Remains found in the Cambridge Upper Greensand, and arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell & Co., Cambridge. 130 pp.
Seeley, 1870b. Remarks on Prof. Owen's monograph on Dimorphodon. Ann. Mag. Nat. Hist. (4). 6, 129-152.
Seeley, 1876. On the British fossil Cretaceous birds. Quarterly Journal of the Geological Society of London. 32, 496-515.
Lydekker, 1891. Catalogue of the Fossil Birds in the British Museum (Natural History). Longmans & Co., London. xxvii + 368 pp.
Brodkorb, 1963. Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bull. Florida State Mus., Bioi. Sci.. 7, 179-293.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Elzanowski and Galton, 1991. Braincase of Enaliornis, an Early Cretaceous bird from England. Journal of Vertebrate Paleontology. 11(1), 90-107.
Galton and Martin, 2002a. Enaliornis, an Early Cretaceous hesperornithiform bird from England, with comments on other Hesperornithiformes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 317-338.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
E? sedgwicki Seeley, 1876
= "Pelargonis sedgwicki" Seeley, 1864
= "Enaliornis sedgwicki" Seeley, 1869
= "Pelagornis sedgwicki" Seeley, 1876
Late Albian, Early Cretaceous
Cambridge Greensand, England
Lectotype
- (SMC B55314) (adult) proximal tibiotarsus (Seeley, 1869)
Paralectotypes- (BMNH A480) (juvenile) proximal tibiotarsus
(SMC B55287) (juvenile) proximal femur (Seeley, 1869)
(SMC B55295) (adult) distal femur (16 mm wide) (Seeley, 1869)
(SMC B55315) (adult) distal tibiotarsus (11.2 mm wide)
Referred- (BMNH A479) (adult) femur (Galton and Martin, 2002b)
(BMNH A482) (adult) distal femur (Galton and Martin, 2002b)
(BMNH A5802; = BMNH A478 in part) (adult) distal femur (Galton and Martin, 2002b)
(BMNH 41790) (adult) tarsometatarsal shaft (Galton and Martin, 2002b)
(SMC B55288) (adult) proximal femur (Seeley, 1869)
(SMC B55289) (juvenile) proximal femur (Seeley, 1869)
(SMC B55297) (juvenile) distal femur (Seeley, 1869)
(SMC B55298) (adult) distal femur (Seeley, 1869)
(SMC B55299) (adult) distal femur (16 mm wide) (Seeley, 1869)
(SMC B55300) (adult) distal femur (Seeley, 1869)
(SMC B55301) (juvenile) distal femur (Seeley, 1869)
(SMC B55302) (adult) incomplete femur (Seeley, 1869)
(SMC B55310) (adult) distal femur (16.3 mm wide) (Seeley, 1869)
(SMC B55320) (adult) distal tarsometatarsus (Seeley, 1869)
(SMC B55332) (adult) distal tarsometatarsus (Seeley, 1869)
(YORYMG 581) (juvenile) proximal tibiotarsus (Galton and Martin, 2002b)
(YORYMG 582) (juvenile) proximal tibiotarsus (Galton and Martin, 2002b)
(YORYMG 583) (adult) distal femur (Galton and Martin, 2002b)
Diagnosis- (after Seeley, 1876) smaller than E. barretti and E. seeleyi.
(after Galton and Martin, 2002b) distal tibiotarsus with small anterior medial condyle.
(suggested) cnemial crest extends laterally significantly past proximal tibial articular surface; medial tibiotarsal condyle wider than lateral condyle.
Other diagnoses- The laterally positioned posterior intercondylar sulcus on the tibiotarsus is also present in E. barretti. Baptornis also has medial and lateral anterior tibiotarsal condyles which are equal in size, while E. barretti also has a small lateral condyle and thus a broad shallow intercondylar fossa.
Comments- SMC B55314 is the proximal tibiotarsus with a cnemial crest listed by Seeley (1869) as "Enaliornis." Brodkorb (1963) designated it the lectotype of Enaliornis sedgwicki. SMC B55295 and 55297-55302 were identified as distal humeri of "Enaliornis" by Seeley (1869), but later as distal femora by Seeley (1876; based on how many distal femora he noted) and explicitly so by Galton and Martin (2002b). SMC B55302 was identified by Seeley (1876) as "another species of bird", and later by Galton and Martin (2002a) as E. barretti. SMC B55288-55289 were identified as "Enaliornis" by Seeley (1869). SMC 55287 is probably "Enaliornis" specimen "d 8 1" of Seeley (1869), as it is the only SMC femur remaining after the others are taken into account. BMNH A479 wasn't originally identified to the species by Seeley (1876), but was listed as a paralectotype by Galton and Martin (2002b). SMC B55310 was identified as "Enaliornis" by Seeley (1869). While the referred femora were no doubt among the many noted to exist by Seeley (24 femora from the Woodwardian Museum now at the SMC; 6 femora from the Jesson collection now at the BMNH), they were not identified to species in that work. BMNH A480 was mentioned by Seeley (1876) as a juvenile proximal tibiotarsus of E. sedgwicki from the Jesson collection, so should be a paralectotype, though it was not listed as such by Galton and Martin (2002b). SMC B55320 and 55332 are two of the three "Enaliornis" distal tibiotarsi listed by Seeley (1869). SMC B55320 and 55332 (and maybe BMNH 41790) are probably some of the several "smaller and less perfect" examples of distal tarsometatarsi at Cambridge, said to have "belonged chiefly to Enaliornis sedgwicki" by Seeley (1876).
SMC B55274 (mistyped B55279 in the figures of Galton and Martin, 2002b) and B55280 are dorsal vertebrae referred to E. sedgwicki by Seeley (1876), but as they differ from hesperornithines, were placed in Avialae incertae sedis by Galton and Martin (2002a, b).
This species has been assigned to Enaliornis by every author since its description, but this has been largely due to barretti and sedgwicki being of similar size, locality and grade. However, the posteromedial ridge on metatarsal II noted by Galton and Martin (2002b) and metatarsal II trochlea which is mostly hidden in anterior view may serve to group these species, seeleyi and Pasquiaornis in a clade (though the ridge is unknown in Pasquiaornis). Also, barretti and sedgwicki share the shallow anterior tibiotarsal intercondylar groove and laterally placed posterior tibiotarsal intercondylar groove (both absent in seeleyi but unknown in Pasquiaornis). Another possibility is that sedgwicki is more closely related to Baptornis and hesperornithids than to Enaliornis. This could be supported by the reduced medial femoral condyle (also present in seeleyi, but absent in Baptornis) and metatarsal IV trochlea which is higher in distal view than trochlea III (shared with Pasquiaornis? tankei as well).
References- Seeley, 1864. On the fossil birds of the Upper Greensand, Palaeocolyntus barretti and Pelargonis sedgwicki. Proc. Cambridge Phil. Soc. 1, 228.
Seeley, 1869. Index to the fossil remains of Aves, Ornithosauria and Reptilia, from the Secondary System of strata arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell & Co.,
Cambridge. 143 pp.
Seeley, 1876. On the British fossil Cretaceous birds. Quarterly Journal of the Geological Society of London. 32, 496-515.
Brodkorb, 1963. Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bull. Florida State Mus., Bioi. Sci.. 7, 179-293.
Galton and Martin, 2002a. Enaliornis, an Early Cretaceous hesperornithiform bird from England, with comments on other Hesperornithiformes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 317-338.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
E? seeleyi Galton and Martin, 2002b
Late Albian, Early Cretaceous
Cambridge Greensand, England

Holotype- (BGS 87935) distal tibiotarsus (12.8 mm wide)
Paratypes- (BGS 87929) (adult) distal femur (16.5 mm wide)
(BMNH A478) (adult) proximal tibiotarsus (Seeley, 1876)
(BMNH A481) (juvenile) proximal tibiotarsus (Seeley, 1876)
(BMNH A483c) (adult) distal femur
(BMNH A484) (juvenile) distal femur
(BMNH A485a) (adult) distal tarsometatarsus
(BMNH A485b) (adult) distal femur, distal tarsometatarsus
(BMNH A5801; = BMNH A478 in part) (adult) distal femur
(BMNH 41792) (adult) distal femur
?(SMC B55283) (adult) posterior synsacrum (Seeley, 1876)
(SMC B55290) (juvenile) proximal femur (Seeley, 1869)
(SMC B55291) (juvenile) proximal femur (Seeley, 1869)
(SMC B55292) (juvenile) proximal femur (Seeley, 1869)
(SMC B55293) (juvenile) proximal femur (Seeley, 1869)
(SMC B55307) (adult) distal femur (18.8 mm wide) (Seeley, 1869)
(SMC B55308) (adult) distal femur (18.8 mm wide) (Seeley, 1869)
(SMC B55317) (adult) distal tibiotarsus (12.8 mm wide) (Seeley, 1869)
(SMC B55318) (adult) proximal tarsometatarsus (10.4 mm) (Seeley, 1869)
(SMC B55319) (adult) proximal tarsometatarsus (Seeley, 1869)
(SMC B55321) (adult) distal tarsometatarsus (Seeley, 1869)
(YORYMG 560) (adult) distal tarsometatarsus
?(YORYMG 585) (adult) braincase (Seeley, 1876)
?(YORYMG 586) (adult) braincase (Elzanowski and Galton, 1991)
(YORYMG 588) (adult) proximal tibiotarsus
(YORYMG 589) (adult) distal tarsometatarsus
Diagnosis- (after Galton and Martin, 2002b) larger than E? sedgwicki and smaller than E. barretti.
Other diagnoses- Contra Galton and Martin (2002b), the cnemial crest is flared laterally a comparable amount to E? sedgwicki, though it primitively does not extend lateral to the proximal tibial articular surface. The centrally positioned posterior intercondylar sulcus and deep and narrow anterior intercondylar fossa on the tibiotarsus are also present in Baptornis and Hesperornis. Rounded anterior tibiotarsal condyles are also present in Hesperornis. The transversely compressed medial tarsometatarsal cotyla is also present in Hesperornis regalis, H. bazhanovi and H. chowi.
Comments- Seeley (1876) first noted he thought the Enaliornis material probably belonged to three species, but only named two- E. barretti and E. sedgwicki. Until Galton and Martin (2002b) named E. seeleyi, only those species were recognized, so seeleyi remains were at least implicitly referred to E. barretti or sedgwicki, though much was never explicitly referred to either species. Much of the E. seeleyi material was originally referred to E. barretti by Seeley (1876) (BMNH A478, SMC B55283, B55290, B55308, B55318, B55319) and Galton and Martin (2002a) (BMNH A478, SMC B55283, B55290). Some was also referred to E. sedgwicki by Galton and Martin (2002a) (SMC B55317, B55318, B55319). Elzanowski and Galton (1991) referred both YORYMG 585 and 586 to E. barretti. SMC B55290-55293 and B55307-55308 were identified as "Enaliornis" by Seeley (1869). While the referred femora were no doubt among the many noted to exist by Seeley (24 femora from the Woodwardian Museum now at the SMC; 6 femora from the Jesson collection now at the BMNH), they were not identified to species in that work. BMNH A5803 is listed as a referred specimen for both E. barretti and E. seeleyi in Galton and Martin's (2002b) material list, but is clearly E. barretti based on the text and figures. Either YORYMG 587 or 588 is the adult proximal tibiotarsus of Enaliornis barretti from the Reed collection mentioned by Seeley (1876). YORYMG 587 is listed as E. seeleyi in Galton and Martin's (2002b) materials list, but is E. barretti based on the text and figures. BMNH A481 was mentioned by Seeley (1876) as a juvenile proximal tibiotarsus of E. sedgwicki from the Jesson collection. SMC B55317 is probably one of the two distal tibiae listed as "Enaliornis" by Seeley (1869), and was mislabeled B55310 by Galton and Martin (2002b) in their discussion of distal tibiotarsal variation. SMC B55321 is one of the three "Enaliornis" distal tibiotarsi listed by Seeley (1869). SMC B55321 (and maybe BMNH A485 a and b) are probably some of the several "smaller and less perfect" examples of distal tarsometatarsi at Cambridge, said to have "belonged chiefly to Enaliornis sedgwicki" by Seeley (1876). "J d 5 1-2" (now SMC B55318-55319) were thought to be distal metacarpals of "Enaliornis" (Seeley, 1869), then proximal fibulae (Seeley, 1976), then proximal ulnae (Furbringer, 1888), but are proximal tarsometatarsi.
seeleyi was named based on material originally referred to Enaliornis, but most of Galton and Martin's (2002b) justification for placing seeleyi in Enaliornis was due to symplesiomorphies (see other diagnoses section of Enaliornis' entry). However, the posteromedial ridge on metatarsal II noted by Galton and Martin (2002b) and metatarsal II trochlea which is mostly hidden in anterior view may serve to group Enaliornis barretti, E? sedgwicki, E? seeleyi and Pasquiaornis in a clade (though the ridge is unknown in Pasquiaornis). Another possibility is that seeleyi is more closely related to Baptornis and hesperornithids than to Enaliornis. This could be supported by the reduced medial femoral condyle (also present in sedgwicki, but absent in Baptornis). In either case, there is no valid published reason to place seeleyi closer to Enaliornis than to Pasquiaornis.
References- Seeley, 1869. Index to the fossil remains of Aves, Ornithosauria and Reptilia, from the Secondary System of strata arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell & Co.,
Cambridge. 143 pp.
Seeley, 1876. On the British fossil Cretaceous birds. Quarterly Journal of the Geological Society of London. 32, 496-515.
Elzanowski and Galton, 1991. Braincase of Enaliornis, an Early Cretaceous bird from England. Journal of Vertebrate Paleontology. 11(1), 90-107.
Galton and Martin, 2002a. Enaliornis, an Early Cretaceous hesperornithiform bird from England, with comments on other Hesperornithiformes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 317-338.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
E? sp. indet. (Seeley, 1869)
Late Albian, Early Cretaceous
Cambridge Greensand, England

Material- (Booth Museum coll.) ends of humeri (Galton, Dyke and Kurochkin, 2009)
(SMC B55296) distal femur (Seeley, 1869)
(SMC B55323) tibiotarsal shaft (Seeley, 1869)
(SMC B55324) tibiotarsal shaft (Seeley, 1869)
(SMC B55325) tibiotarsal shaft (Seeley, 1869)
(SMC B55326) tibiotarsal shaft (Seeley, 1869)
(SMC B55327) tibiotarsal shaft (Seeley, 1869)
(SMC coll.) curved bone fragment (Seeley, 1869)
(SMC coll.) element (Seeley, 1869)
Comments- All of the SMC material was originally referred to "Enaliornis", but may belong to another bird or vertebrate taxon. SMC B55323-B55327 were thought to be metacarpal fragments of "Enaliornis" by Seeley (1869), but were reidentified as tibiotarsal shafts by Galton and Martin (2002b), though not explicitly referred to Enaliornis, let alone a particular species. A Woodwardian Museum specimen noted by Seeley (1869) (J d 2 1) as a "fragment of a curved bone" of "Enaliornis" is presumably at the SMC now, but has not been reidentified in the literature. SMC B55296 was originally identified as a distal humerus of "Enaliornis" by Seeley (1869), but reidentified as a distal femur by Galton and Martin (2002b), though not referred to a particular species. The identity of Woodward Museum specimen "d 10 1", listed as an undetermined element of "Enaliornis" by Seeley (1869) is unknown.
Most recently, Galton (in prep.) will describe seven bird elements from the Booth Museum (mentioned as "Enaliornis and Aves incertae sedis, including ends of humeri"). Galton et al. (2009) state Enaliornis has rudimentary humeral heads, indicating the ends of humeri mentioned are from that taxon.
References- Seeley, 1869. Index to the fossil remains of Aves, Ornithosauria and Reptilia, from the Secondary System of strata arranged in the Woodwardian Museum of the University of Cambridge. Deighton, Bell & Co.,
Cambridge. 143 pp.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
Galton, Dyke and Kurochkin, 2009. Re-analysis of Lower Cretaceous fossil birds from the UK reveals an unexpected diversity. Journal of Vertebrate Paleontology. 29(3), 102A.
Galton, in prep. Additional bird bones (Hesperornithiformes Enaliornis and Aves incertae sedis) from the Early Cretaceous of England. Revue Paleobiologie.

Pasquiaornis Tokaryk, Cumbaa and Storer, 1997
Other diagnoses- Tokaryk et al. (1997) used the less laterally projected trochanteric crest and less mediolaterally expanded proximal femur to distinguish Pasquiaornis from Baptornis, but this is primitive and also found in Enaliornis and Ichthyornis. The intercotylar prominence is anteriorly positioned and overhangs the shaft in Hesperornis and Parahesperornis as well. The trochlea of metatarsal II is posterior to and close to the base of trochlea III in all hesperornithines.
Comments- Both of these species were only briefly described and illustrated by Tokaryk et al. (1997), and not compared to the extremely similar Enaliornis. This leaves them without a valid diagnosis, nor are any characters known which could group them together to the exclusion of Enaliornis. To the contrary, the larger size and metatarsal IV trochlear neck which is placed dorsal to that on trochlea III are characters which P? tankei shares with Baptornis and hesperornithids to the exclusion of P. hardiei. However, officially removing tankei from Pasquiaornis should not be done until the material of both hardiei and tankei is examined in detail, including the Bainbridge River specimens.
P. hardiei Tokaryk, Cumbaa and Storer, 1997
Middle Cenomanian, Late Cretaceous
Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Holotype
- (SMNH P2077.117) tarsometatarsus (54 mm)
Paratype- (SMNH P2077.60) femur (47.5 mm)
Referred- (SMNH P2077.62) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.110) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
?(SMNH P2077.125) (juvenile) distal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2409.1) proximal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2409.9) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2409.11) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2409.49) distal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
?(SMNH P2487.3) distal humerus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2487.7) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
Diagnosis- (after Tokaryk et al., 1997) smaller than P? tankei.
Other diagnoses- Tokaryk et al. (1997) say the medial tarsometatarsal cotyle is "deflected toward shaft", but those of most hesperornithines are angled somewhat as well. The neck of trochlea III being higher anteriorly than that of trochlea IV is primitive, being present in Enaliornis barretti and E? seeleyi as well. The "distal rim" of the femoral head is said to be perpendicular to the shaft, but this does not appear to be true for either the rim of the articular surface or the medial or ventral edges of the head.
Comments- This was first noted as a new species of baptornithid by Cumbaa and Tokaryk (1993) before being described by Tokaryk et al. (1997).
References- Cumbaa and Tokaryk, 1993. Early birds, crocodile tears, and fish tales: Cenomanian and Turonian marine vertebrates from Saskatchewan, Canada. Journal of Vertebrate Paleontology. 13(3), 31A-32A.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
P? tankei Tokaryk, Cumbaa and Storer, 1997
Middle Cenomanian, Late Cretaceous
Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Holotype
- (SMNH P2077.63) incomplete tarsometatarsus (85.6 mm)
Paratype- (SMNH P2077.108) femur (64.5 mm)
Referred- (SMNH P2077.10) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.72) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.79) distal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.107) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.109) femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.113) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.116) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.118) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.119) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.120) quadrate, distal tibiotarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.123) partial pelvic element (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.124) partial pelvic element (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2077.127) partial pelvic element (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2409.2) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2409.3) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2467.2) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2467.3) distal femur (Tokaryk, Cumbaa and Storer, 1997)
?(SMNH P2467.8) distal humerus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2487.2) femur (Tokaryk, Cumbaa and Storer, 1997)
?(SMNH P2487.4) distal humerus (Tokaryk, Cumbaa and Storer, 1997)
(SMNH P2487.8) proximal tibiotarsus (Tokaryk, Cumbaa and Storer, 1997)
Diagnosis- (after Tokaryk et al., 1997) larger than P. hardiei.
Other diagnoses- Tokaryk et al. (1997) also state the "distal rim" of the femoral head is slanted toward the shaft, but the meaning of this is uncertain. The medial tarsometatarsal cotyle is said to be level in medial view, which is unlike Hesperornis and Parahesperornis, but similar to Gansus and Enaliornis? seeleyi, so may be plesiomorphic. The neck of trochlea III being lower anteriorly than that of trochlea IV is present in Enaliornis? sedgwicki, Parahesperornis and Hesperornis as well.
Comments- This was first noted as a new species of baptornithid by Cumbaa and Tokaryk (1993) before being described by Tokaryk et al. (1997). As noted in the Pasquiaornis comments, tankei may not belong to that genus and may be more closely related to Baptornis and hesperornithids.
References- Cumbaa and Tokaryk, 1993. Early birds, crocodile tears, and fish tales: Cenomanian and Turonian marine vertebrates from Saskatchewan, Canada. Journal of Vertebrate Paleontology. 13(3), 31A-32A.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
P. spp. (Tokaryk, Cumbaa and Storer, 1997)
Middle Cenomanian, Late Cretaceous
Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada

Material- over 250 elements including cranial elements, mandibular elements, few dozen teeth, vertebrae, scapula, coracoid, radius, ulna, carpometacarpus, pelvis, tibiotarsus, fibula and phalanges (Cumbaa et al., 2006)
Comments- Tokaryk et al. (1997) reported that in 1994 and 1995 numerous bird fossils similar to Pasquiaornis were discovered at the Bainbridge River Bonebed. Cumbaa et al. (2006) states hundreds of bird specimens are known, mostly hesperornithine, and illustrates four teeth. Sanchez et al. (2009) note both P. hardiei and P? tankei are represented in this material, as well as a possible new species of Pasquiaornis. The material is still being researched.
References- Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
Sanchez, Cumbaa and Schroder-Adams, 2009. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Journal of Vertebrate Paleontology. 29(3), 175A.

Hesperornithoidea Marsh, 1872 vide Shufeldt, 1903
Definition- (Baptornis advenus + Hesperornis regalis) (Martyniuk, 2012)
Diagnosis- (proposed) quadratojugal buttress on quadrate (absent in Hesperornis regalis; unknown in more basal hesperornithines); articular surfaces of dorsal vertebrae broad and trapezoidal; pygostyle less than two caudal vertebrae in length (unknown in more basal hesperornithines); medial area of coracoid depressed where supracoracoid foramen is (also in Apsaravis; unknown in more basal hesperornithines); sternum lacks keel (unknown in more basal hesperornithines); deltopectoral crest reduced in height (also in Patagopteryx and Aves; unknown in more basal hesperornithines); bicipital crest lacks fossae (also in Songlingornithidae and Patagopteryx; unknown in more basal hesperornithines); brachial fossa on humerus poorly developed (also in Apsaravis); humerus reduced to have indistinct distal condyles; femur very robust; tarsometatarsus less than five times longer than broad; intercotylar prominence well developed (also in Ichthyornis and Aves);
Comments- Shufeldt (1903) named Hesperornithoidea to contain both Enaliornithidae and Hesperornithidae. A clade to the exclusion of Enaliornis was proposed by Martin (1984) based on heterocoelous dorsal centra, but the amphicoelous presacrals referred to Enaliornis are now thought to belong to another taxon (Galton and Martin, 2002b).
References- Shufeldt, 1903. On the classification of certain groups of birds. The American Naturalist. 37, 33-64.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Hesperornis? macdonaldi Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US

Holotype- (LACM 9728) femur (44.7 mm)
Diagnosis- (after Martin and Lim, 2002) small size, with tarsometatarsal length estimated at <60 mm (also in Pasquiaornis hardiei).
Other diagnoses- Martin and Lim (2002) also diagnosed this species based on the deeply concave lateral femoral margin, which is also present in Hesperornis regalis.
Comments- Bryant first mentions this specimen as "several femora including some very small (and presumably very young) ones collected by myself and others working with a Los Angeles County Museum field party in 1964", though it was undescribed at the time. Martin and Lim believe the holotype is an adult due to its well formed articular surfaces.
This species was described in Hesperornis by Martin and Lim. However it has an uncertain placement, as the femora of hesperornithids besides "Baptornis" varneri and Hesperornis regalis are still undescribed, and mostly unpreserved. The extreme robusticity is shared with H. regalis, but seemingly not H. bazhanovi or Parahesperornis. The strong anteroposterior compression of the shaft is also shared with H. regalis but not "B." varneri or H. crassipes. However, the medial condyle is not distally projected, unlike "B." varneri and H. regalis. The small size is unlike Hesperornithidae.
References- Bryant, 1983. Hesperornis in Alaska. Paleobios. 40, 1-8.
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.

Judinornis Nessov and Borkin, 1983
J. nogontsavensis Nessov and Borkin, 1983
Late Campanian-Early Maastrichtian, Late Cretaceous
Nemegt Formation, Mongolia
Holotype
- (PO 3389) incomplete last dorsal vertebra (14.1 mm)
Diagnosis- (proposed) highly elongate dorsal vertebrae (~2.5 longer than posteriorly high).
Other diagnoses- Kurochkin (2000) listed dorsal central articular surfaces transversely expanded, ventral surface of dorsal centrum transversely narrow in middle and expanded posteriorly, and prezygapophyses with little transverse separation in his diagnosis, but then correctly noted these are general hesperornithine characters in the comments section. In addition, he listed the trapezoidal dorsal central articular surfaces in his diagnosis, but these are found in other hesperornithines as well.
Comments- Nessov and Borkin (1983) originally referred Judinornis to the Charadriiformes, but it was reassigned to the Baptornithidae without evidence by Nessov (1986). Kurochkin (2001) listed characters shared with Baptornis, but these are plesiomorphic as noted in the Baptornithidae comments. The holotype is indeed extremely similar to Baptornis, though no synapomorphies seem evident. The low central articular surfaces with projecting ventrolateral corners indicate it is more derived than Enaliornis. Several characters are more similar to Baptornis and Parascaniornis than to Hesperornis- the prezygapophysis is elongate and well separated from the centrum in lateral view; ventral centrum surface is transversely constricted; the transverse processes extend further anteriorly.
References- Nessov and Borkin, 1983. [New records of bird bones from Cretaceous of Mongolia and Middle Asia] Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 116, 108-110.
Nessov, 1986. The first record of the Late Cretaceous bird Ichthyornis in the Old World and some other bird bones from the Cretaceous and Paleogene of Soviet Middle Asia. Proc. Zool. Inst. USSR Acad. Sci.. 147, 31-38.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.

Parascaniornis Lambrecht, 1933
P. stensioei Lambrecht, 1933
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Ivo Klack, Sweden
Holotype
- (MGUH 1908.214) posterior dorsal vertebra (15 mm)
Referred- ?(RM PZ R1261) distal tarsometatarsus (Rees and Lindgren, 2005)
Comments- The holotype was discovered in 1908 and described by Lambrecht (1933) as a "scaniornithid" (Scaniornis is a Paleocene bird variously allied with ciconiiforms or phoenicopteriforms). Lambrecht originally spelled the species stensiöi, which must be corrected to stensioei according to ICZN Article 32.5.2.1- "in a name published before 1985 and based upon a German word, the umlaut sign is deleted from a vowel and the letter "e" is to be inserted after that vowel." Howard (1950) believed Parascaniornis was a phoenicopteriform, but it was reidentified as a hesperornithine by Nessov (in Mourer-Chauvire, 1990) and Nessov and Prizemlin (1991). Rees and Lindgren (2005) reexamined this vertebra and found it to be identical to Baptornis advenus and SMNH P2306.2 of the Judith River Group, except for the more horizontally directed prezygapophyses. They viewed it as indeterminate within Baptornis and called it Baptornis sp., but as Ford (online, 1995) notes, you cannot sink a named species into "sp.". Instead, it would be named Baptornis stensioei, though this combination is not yet published. However, Rees and Lindgren did not list any derived characters that could be used to place stensioei in Baptornis, nor even any shared primitive characters. The low central articular surfaces with projecting ventrolateral corners indicate it is more derived than Enaliornis. In elongation, Parascansiornis is similar to Baptornis, more elongate than Hesperornis, but less than Judinornis. The prezygapophysis is elongate and well separated from the centrum in lateral view, as in Baptornis and Judinornis, but unlike Hesperornis. The ventral surface is transversely constricted and the transverse processes extend further anteriorly as in Baptornis and especially Judinornis, but less than Hesperornis. As Parascaniornis is roughly equally similar to Baptornis and Judinornis, and shares to obvious apomorphies with either, it is here retained in its own genus.
References- Lambrecht, 1933. Handbuch der Paläornithologie. Berlin, Gebrüder Borntraeger. 1024 pp.
Howard, 1950. Fossil evidence of avian evolution. Ibis. 92, 1-21.
Mourer-Chauvire, 1990. Society of Avian Paleontology and Evolution Information Newsletter. 4.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107. [In Russian].
Nessov, 1992. [Flightless birds of meridional Late Cretaceous sea straits of North America, Scandinavia, Russia and Kazakhstan as indicators of features of oceanic circulation.] Byulleten Moskovskogo Obshchestva Ispytatelet Prirody Otdel Geologicheskii. 67, 78-83.
Rees and Lindgren, 1999. Early Campanian hesperornithiform birds from the Kristianstad Basin, southern Sweden. in Hoch and Brantsen (eds). Secondary adaptation to life in water. Abstracts. University of Copenhagen, Copenhagen. 53.
Ford, online 2005. http://www.dinohunter.info/html/articles2005.htm
Rees and Lindgren, 2005. Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 48(6), 1321-1329.

Hesperornithes indet. (Tokaryk and Harington, 1992)
Late Campanian, Late Cretaceous
Judith River Group, Saskatchewan, Canada
Material
- (SMNH P2306.2) fourth dorsal vertebra (21.2 mm)
Comments- This specimen was discovered in 1975-1976 and was described as Baptornis sp. by Tokaryk and Harington (1992). Of the characters used to refer this to Baptornis, the heterocoely of dorsal four is present in all hesperornithines. The narrower and lower posterior central articular surface (compared to centrum length) is plesiomorphic, being present in Enaliornis and Judinornis as well, while the lower anterior central articular surface and small parapophysis are also present in Judinornis. The centrally placed hypapophysis is also present in Hesperornis. However, as the centrum is trapezoidal, it is probably more derived than Enaliornis.
Reference- Tokaryk and Harington, 1992. Baptornis sp. (Aves: Hesperornithiformes) from the Judith River Formation (Campanian) of Saskatchewan, Canada. Journal of Paleontology. 66(6), 1010-1012.

unnamed hesperornithine (Martin, 1983)
Middle Cenomanian, Late Cretaceous
Basal Lincoln Limestone Member of the Greenhorn Limestone, Kansas, US
Material
- (FHSM VP-6318) proximal and distal tarsometatarsus (16.7 mm wide proximally)
Comments- This was discovered in 1979 and mentioned by Martin (1983) and Tokaryk et al. (1997). Though the description was listed on the Oceans of Kansas website as set to appear in volume 28(4) of JVP, it was not published until volume 29(3). Everhart and Bell (2009) refer this specimen to Baptornithidae based on several problematic characters (see Baptornithidae other diagnoses). While it does seem to be the same grade as Baptornis, there are currently no synapomorphies to link the two taxa.
References- Martin, 1983. The origin and early radiation of birds. in Bush and Clark (eds.). Perspectives in Ornithology. Cambridge University Press, Cambridge. 291-338.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
http://www.oceansofkansas.com/Hesperornis.html
Everhart and Bell, 2009. A hesperornithiform limb bone from the basal Greenhorn Formation (Late Cretaceous; Middle Cenomanian) of north central Kansas. Journal of Vertebrate Paleontology. 29(3), 952-956.

Baptornithidae American Ornithologist Union, 1910
Definition- (Baptornis advenus ~ Hesperornis regalis) (Martyniuk, 2012)
Other diagnoses- Martin and Tate (1976) included several characters in their diagnosis for Baptornithidae, in which they included Baptornis and Neogaeornis (now thought to be a gaviiform). The character "fully heterocoelous vertebrae" was supposed to distinguish them from Enaliornis, but the amphicoelous presacral vertebrae assigned to that taxon are now thought to belong to another bird. The angled uncinate processes and elongate pygostyle are unknown for any putative baptornithid except B. advenus, so are made an apomorphy of that species here. The highly compressed pygostyle and uncompressed patella of Baptornis advenus are unlike Hesperornis, but unknown in other basal ornithuromorphs, so are provisionally made apomorphies of that species. The unfused chevrons ("intercentral bones"), slender coracoid, elongate preacetabular process, metatarsal II trochlea which is less rotated ventromedially, open groove between metatarsal trochlea III and IV, and comparatively small metatarsal trochlea IV are primitive characters.
Tokaryk et al. (1997) use some of the previous characters and the slender femora to place Pasquiaornis in the Baptornithidae, but this is also primitive.
Kurochkin (2000) noted three characters he thought united Baptornis with Judinornis in the Baptornithidae. Of these, a pneumatic pit between the transverse process and prezygapophysis on dorsal vertebrae is probably plesiomorphic, being present in Ichthyornis as well. A ventrally flat centrum is only found in the last dorsal of Baptornis advenus, as more anterior vertebrae are similar to Hesperornis in having prominent hyapophyses. Yet the last dorsal of Enaliornis also lacks hyapophyses, as do the last few dorsals of Ichthyornis and Gansus, so this is a plesiomorphy. Some presacrals of Baptornis advenus and "B." varneri resemble Judinornis in having a central pit on their articular surfaces. While these seem to be absent in the two preserved presacrals of Enaliornis, they are likely to be remnants of the amphicoelous condition in more basal ornithuromorphs like Ichthyornis, Gansus and Yixianornis.
Martin and Cordes-Person (2007) note other characters supposedly diagnostic of baptornithids. A smooth femoral patellar groove, subcircular femoral shaft, and unreduced metatarsal II trochlea are plesiomorphic. The cervical vertebrae of "Baptornis" varneri are said to be like those of B. advenus in being more elongate than Hesperornis (and Parahesperornis), but this does not seem to be true based on the photograph.
Everhart and Bell (2009) diagnosed a Baptornithidae including Baptornis, Pasquiaornis and FHSM VP-6318. The rounded intercotylar prominence is a plesiomorphy compared to Hesperornis, while the intermediate height between Enaliornis and Hesperornis cannot be used as a synapomorphy to exclude both of those taxa from a baptornithid clade. Similarly, the indentations which partially constrict the distal vascular foramen between metatarsals III and IV are an intermediate state between the unconstricted Enaliornis and the distally closed foramen in Hesperornis, and are also seen in Parahesperornis. The infracotylar fossa and anteriorly tilted cotyla are present in hesperornithids as well. Contra Everhart and Bell, Enaliornis barretti and E? seeleyi also have the groove on trochlea III deeper than that on trochlea IV.
Comments- Baptornithidae has been a paraphyletic taxon for hesperornithines which are more basal than Parahesperornis, but there is currently no evidence any other species was more closely related to Baptornis than to Hesperornis. Taxa which have been assigned to Baptornithidae in the past include Eupterornis (Romer, 1933), Neogaeornis (Brodkorb, 1963), Judinornis (Nessov, 1986) and Pasquiaornis (Tokaryk et al., 1997). The former two are now thought to be gaviiforms (Brodkorb, 1963 and Olson, 1992 respectively), while the latter two are Baptornis-grade hesperornithines. Everhart and Bell (2009) described FHSM VP-6318 as a baptornithid, but their evidence was flawed.
References- American Ornithologist Union, 1910. Checklist of North American birds. Third edition. American Ornithologist’s Union, New York. 430 pp.
Romer, 1933. Vertebrate Paleontology. University of Chicago Press, Chicago.
Brodkorb, 1963. Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bull. Florida State Mus., Bioi. Sci.. 7, 179-293.
Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). in Olson (ed). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Nessov, 1986. The first record of the Late Cretaceous bird Ichthyornis in the Old World and some other bird bones from the Cretaceous and Paleogene of Soviet Middle Asia. Proc. Zool. Inst. USSR Acad. Sci.. 147, 31-38.
Olson, 1992. Neogaeornis wetzeli Lambrecht, a Cretaceous loon from Chile (Aves: Gaviidae). Journal of Vertebrate Paleontology. 12, 122-124.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Everhart and Bell, 2009. A hesperornithiform limb bone from the basal Greenhorn Formation (Late Cretaceous; Middle Cenomanian) of north central Kansas. Journal of Vertebrate Paleontology. 29(3), 952-956.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Baptornis Marsh, 1877
Diagnosis- as for B. advenus.
Other diagnoses- Martin and Tate (1976) used the size as a diagnostic character of Baptornis, but it is similar to Pasquiaornis tankei. The greatly reduced forelimb is present in hesperornithids as well, while the retention of the radius and ulna are plesiomorphies also present in Pasquiaornis. Martin and Tate also distinguished Baptornis from Neogaeornis by having a less compressed tarsometatarsus, but this is true of all hesperornithines.
Tokaryk and Harington (1992) include a few dorsal characters in their diagnosis. The heterocoely of dorsal four is present in all hesperornithines. The narrower and lower posterior central articular surface (compared to centrum length) is plesiomorphic, being present in Enaliornis and Judinornis as well, while the lower anterior central articular surface and small parapophysis are also present in Judinornis. The centrally placed hypapophysis is also present in Hesperornis.
Martin and Cordes-Person (2007) list several synapomorphies of Baptornis advenus and "B." varneri. As noted under Baptornithidae, the cervical vertebrae of "B." varneri do not appear to be more elongate than those of Hesperornis, contra the text. The absence of "vertebrarterial canals" (= transverse foramina) in Baptornis seems implausible, as all theropods have diapophyseal and parapophyseal articulations with their cervical ribs, and may refer to an absence of fused cervical ribs instead. This is affected by ontogeny, and was not stated to be certainly absent in B. advenus by Martin and Tate in any case. Heterocoelous dorsal vertebrae and medial femoral condyles which are smaller than the lateral condyle are present in all hesperornithines. Pits in the posterior central articular surfaces of presacral centra, a subcircular femoral cross section, a smooth patellar groove and subequally sized tarsometatarsal trochlea are primitive characters.
Comments- Several other taxa have been referred to Baptornis in the past. Kurochkin (1988) referred a distal tibiotarsus from the Nemegt Formation of Mongolia to Baptornis sp., but this is here shown to resemble Enaliornis? seeleyi as well and thus referred to Hesperornithes incertae sedis. Tokaryk and Harington (1992) described a dorsal vertebra from the Judith River Group of Asakatchewan as Baptornis sp., but the characters they used were symplesiomorphic and the specimen is here referred to the Baptornis + Hesperornis clade as a nomen dubium. Nessov (1997) thought some small hesperornithine material from the Zhuralovskaya Svita of Kazakhstan could be referrable to Baptornis, but this undescribed material is here referred to Hesperornithes incertae sedis. Rees and Lindgren (2005) placed Parascaniornis stensioei in Baptornis as B. sp., which as noted in its description here was not based on any synapomorphies. Most recently, a specimen was described as the new species Baptornis varneri by Martin and Cordes-Person (2007), but this is based on a mix of symplesiomorphies and synapomorphies of more inclusive clades as noted above. The species is here placed as a basal hesperornithid.
References- Marsh, 1877. Characters of the Odontornithes, with notice of a new allied genus. American Journal of Science. 14, 85-87.
Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). in Olson (ed). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Kurochkin, 1988. [Cretaceous birds of Mongolia and their significance for study of the phylogeny of class Aves.] Trudy Sovmestnoi Sovetsko-Mongolskoi Paleontologicheskoi Ekspeditsii. 34, 33-42.
Tokaryk and Harington, 1992. Baptornis sp. (Aves: Hesperornithiformes) from the Judith River Formation (Campanian) of Saskatchewan, Canada. Journal of Paleontology. 66(6), 1010-1012.
Nessov, 1997. Cretaceous non-marine vertebrates of Northern Eurasia. St. Petersburg State University, St-Petersburg. 218 pp.
Rees and Lindgren, 2005. Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 48(6), 1321-1329.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
B. advenus Marsh, 1877
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Lectotype- (YPM 1465) distal tarsometatarsus
Paralectotype- (YPM 5768; = YPM 1465 in part) (juvenile) proximal tarsometatarsus
Referred- (AMNH 5101) premaxillary fragment, frontal fragment, ventral quadrate (lost), atlantal intercentrum, axis, fourteen cervical vertebrae, six dorsal vertebrae, dorsal rib fragments, synsacrum, four proximal caudal vertebrae, mid caudal vertebra, partial pelvis (Martin and Tate, 1976)
(FMNH 395) posterior mandible, sixth dorsal vertebra (18.7 mm), dorsal rib fragments, synsacrum, five mid caudal vertebrae, pygostyle, pelvic material, femora (72 mm), tibiotarsi (194 mm), fibula, metatarsal I (14 mm), phalanx I-1 (22 mm), tarsometatarsus (83 mm), phalanx II-2 (31.7 mm), phalanx III-3 (20.5 mm), phalanx IV-1 (37 mm), phalanx IV-2 (25 mm), phalanx IV-3 (23 mm), phalanx IV-4 (23 mm), six pedal phalanges, two pedal unguals (Martin and Tate, 1976)
(Fick Fossil Museum coll.) premaxillary fragment(?), femur, proximal tibiotarsus, tibiotarsal shaft, distal tibiotarsus, proximal fibula, two tarsometatarsi, three incomplete tarsometatarsi, eleven fragments (Martin and Tate, 1976)
(KUVP 2290) six cervical vertebrae, dorsal vertebrae, dorsal rib fragments, synsacrum, proximal scapula, incomplete coracoid (53 mm), incomplete humerus (~118 mm), radius (20.5 mm), ulna (21.6 mm), anterior ilium, femora (75 mm), patella (20.5 mm), partial tibiotarsi, proximal fibula, partial tarsometatarsus (~83 mm) (Lucas, 1903)
(KUVP 16112) (juvenile) premaxilla, eighth cervical vertebra, thirteenth cervical vertebra, fourteenth cervical vertebra, three partial cervical vertebrae, second dorsal vertebra (~20 mm), third dorsal vertebra (21 mm), fourth dorsal vertebra (~22 mm), fifth dorsal vertebra (22 mm), dorsal rib fragments, synsacral fragment, pelvic material, proximal femora, distal femur, tibial shaft, distal tibiae, incomplete metatarsi, two proximal pedal phalanges, one distal pedal phalanx (Walker, 1967)
(UNSM 20030) fifteenth cervical vertebra, sixteenth cervical vertebra, first dorsal vertebra (21 mm), second dorsal vertebra (21.5 mm), third dorsal vertebra (21.5 mm), fourth dorsal vertebra (22 mm), fifth dorsal vertebra (22 mm), sixth dorsal vertebra (19.5 mm), four dorsal ribs, six uncinate processes, five mid caudal vertebrae, pygostyle, partial coracoid, partial sternum, four sternal ribs, incomplete humerus, ilium, pubis, ischium, femur (71 mm), patellae (19 mm), tibiotarsi (195 mm), fibulae, tarsometatarsi (84 mm), phalanx III-1 (37 mm), phalanx III-2 (28.2 mm), phalanx IV-1 (37 mm), phalanx IV-2 (25.5 mm), phalanx IV-3 (24 mm), pedal phalanx, pedal skin impression, cololites (Martin and Tate, 1976)
(YPM 1467) femur, tibiotarsus (~125 mm) (Marsh, 1880)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, Manitoba, Canada

? tibiotarsus and/or tarsometatarsus (Aotsuka et al., 2012)
Diagnosis- (after Marsh, 1880) prominent medial tibial crest.
(after Lucas, 1903) cervical vertebrae highly elongate; procoracoid process absent.
(proposed) uncinate processes angled dorsally at base; pygostyle longer than four vertebrae; highly transversely compressed pygostyle; pubis and ischium appressed; patella transversely wider than deep; proximolateral fossa for fibula on tibiotarsus narrow and deep; intertrochlear grooves on tarsometatarsus not extending proximal to trochlea II.
Other diagnoses- Marsh (1877) mentions only plesiomorphies- metatarsal trochlea III and IV subequal in width and length.
Marsh (1880) later mentions the slender femur, which is also plesiomorphic.
Lucas (1903) lists several features which differ from Hesperornis, but most are plesiomorphic- short sacrum; elongate coracoid; radius and ulna present; femur not projected transversely; high cnemial crest.
The extreme transverse slenderness of the tarsometatarsus noted by Shufeldt (1915) is also present in Pasquiaornis hardiei.
Martin and Cordes-Person (2007) listed several characters for B. advenus, most of which are plesiomorphic and also present in "B." varneri- heterocoelous dorsal vertebrae; subcircular femoral cross section; smooth patellar groove in femur; tarsometatarsus with proximal cap; metatarsal II trochlea which is less rotated ventromedially. The lack of crescent and peg articulations on pedal digit IV phalanges is also primitive, though unpreserved in "B." varneri and other non-hesperornithid hesperornithines. The femoral medial condyle is actually larger than in "B." varneri (as in Pasquiaornis), not smaller as in Enaliornis and Hesperornis. The distal tibiotarsus being angled anteriorly is plesiomorphic as well, being shared with Parahesperornis.
Comments- The lectotype and paralectotype were discovered in 1876 and described by Marsh in 1877, though Shufeldt (1915) and Martin and Tate (1976) confirmed they were from different individuals, as YPM 1465 is adult and YPM 5768 is juvenile. They designated YPM 1465 the lectotype. KUVP 20030 was discovered in 1936, but not described until 1976 by Martin and Tate. The large humerus reported by Walker (1967) for KUVP 16112 is a tibial shaft. The cololites of UNSM 20030 include a jaw of the fish Enchodus cf. parvus. Elzanowski et al. (2001) state that there is no quadrate catalogued under AMNH 5101, nor could any record of it be found there. They furthermore believe that the quadrate was too small to be derived from the specimen and question its referral to Baptornis, though they do believe it is an "odontognath." Martin and Tate (1976) noted they examined specimens at the Fick Fossil Museum, which are not described further, but are photographed on Oceans of Kansas. Chiappe (1996) listed KUVP 2295 as a Baptornis specimen, but probably meant KUVP 2290.
References- Marsh, 1877. Characters of the Odontornithes, with notice of a new allied genus. American Journal of Science. 14, 85-87.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Brown, 1911. Notes on the restorations of the Cretaceous birds Hesperornis and Baptornis. Annals of the New York Academy of Sciences. 20, 401.
Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Walker, 1967. Revival of interest in the toothed birds of Kansas. Transactions of the Kansas Academy of Sciences. 70(1), 60-66.
Martin and Tate, 1969. New information on Baptornis advenus. Proceedings of the Nebraska Academy of Sciences (79th Annual Meeting). 49-50.
Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). in Olson (ed). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Martin and Bonner, 1977. An immature specimen of Baptornis advenus from the Cretaceous of Kansas. The Auk. 94, 787-789.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Chiappe, 1996. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Everhart, online 2000-2009. http://www.oceansofkansas.com/Birds/fickhesp.jpg
Elzanowski, Paul and Stidham, 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology. 20(4), 712-719.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Everhart, online 2008-2009. http://www.oceansofkansas.com/Baptornis.html
Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in Southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.

Hesperornithidae Marsh, 1872
= Asiahesperornithinae Nessov and Prizemlin, 1991
Definition- (Hesperornis regalis <- Baptornis advenus) (Clarke, 2004)
Diagnosis- (proposed) proximal tibiotarsal shaft gradually expanded anteroposteriorly; elongate fibular crest on tibiotarsus (~59% of tibiotarsal length); large size (tarsometatarsus >20 mm in proximal transverse width).
Comments- Marsh (1872) originally called this family Hesperornidae, but this had to be corrected to Hesperornithidae. Nessov and Prizemlin's (1991) taxon Asiahesperornithinae is redundant as Asiahesperornis seems to be nested within Hesperornis itself.
References- Marsh, 1872. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3, 359-365.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107 (in Russian).
Bogdanovich, 2003. Morphologic aspect of phylogeny of Hesperornithidae (Ornithurae, Aves). Vestnik zoologii. 37(6), 65-71.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286: 1-179.

Brodavidae Martin, Kurochkin and Tokaryk, 2012
Definition- (Brodavis americanus <- Hesperornis regalis) (Martyniuk, 2012)
References- Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Brodavis Martin, Kurochkin and Tokaryk, 2012
Comments- Nessov (1992) first commented on the possibility of small volant hesperornithines based on small elements in North American museums from the Late Campanian and Maastrichtian of the US and Canada. No details were given, but Martin et al. (2012) eventually described these tarsometatarsi including one from the Nemegt Formation previously described by Kurochkin (2000) as species of the new genus Brodavis. Further study will be necessary to determine whether the diagnosis provided by Martin et al. includes synapomorphic characters, or merely symplesiomorphies, and thus whether B? baileyi, B? varneri and B? mongoliensis are properly referred to this genus.
References- Nessov, 1992. [Flightless birds of meridional Late Cretaceous sea straits of North America, Scandinavia, Russia and Kazakhstan as indicators of features of oceanic circulation.] Byulleten Moskovskogo Obshchestva Ispytatelet Prirody Otdel Geologicheskii. 67, 78-83.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
B. americanus Martin, Kurochkin and Tokaryk, 2012
Late Maastrichtian, Late Cretaceous
Frenchman Formation, Saskatchewan, Canada
Holotype
- (RSM P2315.1) incomplete tarsometatarsus
Diagnosis- (after Martin et al., 2012) facet for metatarsal one placed below the middle of tarsometatarsus; metatarsal shaft broader and more robust than in B. baileyi but is smaller and less robust than B. varneri; trochlea for digit IV swollen proximally, being slightly broader than the trochlea for digit III, with broad and flat anterodistal surface.
Reference- Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
B? baileyi Martin, Kurochkin and Tokaryk, 2012
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, South Dakota, US
Holotype
- (USNM 50665) incomplete tarsometatarsus
Diagnosis- (after Martin et al., 2012) shaft of the tarsometatarsus more slender than in B. americanus with trochlea for digit IV less expanded at base; trochlea for digit II more elevated proximally at base and placed more behind trochlea for digit III; outer anterior ridge of shaft extending more distally; proximal nutrient foramina reduced practically to absence.
Reference- Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
B? varneri (Martin and Cordes-Person, 2007) Martin, Kurochkin and Tokaryk, 2012
= Baptornis varneri Martin and Cordes-Person, 2007
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US
Holotype
- (SDSM 68430) (adult) anterior (~3-6) cervical vertebra, mid (~7-10) cervical vertebra, fourteenth cervical vertebra, fifteenth cervical vertebra, sixteenth cervical vertebra, seventeenth cervical vertebra, posterior cervical or anterior dorsal vertebrae, first dorsal vertebra, two dorsal ribs, posterior synsacrum, posterior ilia, pubes, ischia, partial femora, tibiotarsus (206.47 mm), fibula, tarsometatarsus (96.13 mm)
Diagnosis- (after Martin and Cordes-Person, 2007) tarsometatarsus more robust than other hesperornithines.
Other diagnoses- Martin and Cordes-Person (2007) list elongate cervical vertebrae as a character of this species, but they are shorter than in B. advenus. The capitulum and tuberculum of the illustrated dorsal rib are similarly placed to B. advenus, not necessarily more separated as stated by the authors, especially when one considers that only two proximal rib portions are photographed for B. advenus. The indistinct antitrochanter is a plesiomorphy shared with Enaliornis barretti, while the open acetabulum is also a plesiomorphy shared with taxa such as Ichthyornis and Apsaravis. The well separated pubis and ischium is a plesiomorphy found in Enaliornis, Parahesperornis and Hesperornis. The proximolateral ischial fossa is said to be more shallow than in B. advenus and Hesperornis, but does not seem so in the photo. A broad popliteal fossa is primitive, being present in Enaliornis, Hesperornis and Pasquiaornis? tankei (but perhaps not P. hardiei), whereas the fossa does not appear smoother in "B." varneri than in other hesperornithines. A shallow popliteal fossa is also present in Enaliornis, while a wide intercondylar fossa is also present in Enaliornis and Hesperornis. The prominent medial femoral condyle is also present in Enaliornis? sedgwicki, and the lateral condyle does not appear more "high and distinct" than in B. advenus. The anteroposteriorly expanded proximal tibiotarsus and elongate fibular crest (~59% of tibiotarsal length) are shared with Hesperornis. The straightness of the fibular crest might refer to the fact it doesn't seem to curve distally onto the anterior shaft as in B. advenus, but polarity is difficult to establish. Enaliornis shares the shallow proximolateral fossa for the fibula, making the opposite state a possible apomorphy of B. advenus. Contra Martin and Cordes-Person, the distal tibiotarsus does not curve medially more than in B. advenus. Proximal foramina are present in Parahesperornis and Hesperornis as well (and Pasquiaornis? tankei), as noted in the description of FHSM VP-17312, making the reported absence in B. advenus probably due to incomplete preparation. Elongate intertrochlear grooves are also found in Enaliornis, Pasquiaornis, Parahesperornis and Hesperornis, making their absence an apomorphy of B. advenus. The tarsometatarsi of all hesperornithines are waisted transversely just proximal to trochlea II as in B. varneri.
Comments- This specimen was discovered in 1991 and first published in an abstract by Martin and Varner (1992), to be formally described and named by Martin and Cordes-Person (2007). While most published references refer the species to Baptornis, this is based on a mix of symplesiomorphies and synapomorphies of more inclusive clades as noted in the Baptornis other diagnoses section. In contrast, there is some support for placing this species as the basalmost hesperornithid, as seen in the Hesperornithidae diagnosis above. Martin et al. (2012) included it in their new genus Brodavis based on "overall shape of the tarsometatarsus" and the symplesiomorphic small metatarsal IV trochlea compared to Hesperornis. As this is vague and problematic reasoning and the authors themselves state it "should probably have its own generic designation", this assignment is provisional.
References- Martin and Varner, 1992. The highest stratigraphic occurrence of the fossil bird Baptornis. Proceedings of the South Dakota Academy of Science. 71, 167 (abstract).
Person and Martin, 2004. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. Geological Society of America Abstracts with Programs. 36(4), 80.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
B? mongoliensis Martin, Kurochkin and Tokaryk, 2012
Late Campanian-Early Maastrichtian, Late Cretaceous
Nemegt Formation, Mongolia

Holotype- (PIN 4491-8) incomplete tarsometatarsus (Kurochkin, 2000)
Diagnosis- (after Martin et al., 2012) xxternal cotyla in proximal head of the tarsometatarsus expands anteroposteriorly, with anterior and posterior parts inclined distally; proximal nutrient foramina are well developed; metatarsal facet for digit I placed almost in the middle of the tarsometatarsus; metatarsal shaft slender; transverse section in the middle of shaft close to quadrangular.
Comments- The holotype was discovered in 1987. Kurochkin (2000) described it and mentioned a small mandible and cervical vertebra which were "somewhat different" from other hesperornithines. He referred these to "Hesperornithiformes fam. nov." though he did not list any diagnostic characters. Kurochkin also related these to small hesperornithine remains from the Zhuralovskaya Svita (Mourer-Chauvire, 1992), which are presently undescribed and generally referred to Baptornithidae. The mandible and vertebral may be the same taxon as B. mongoliensis and IGM 100/1311, which are of similar size and also have thinner bone walls than Baptornis or Hesperornis.
References- Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.

unnamed clade (Parahesperornis alexi + Hesperornis regalis)
Diagnosis- (proposed) elongate orbital process on quadrate (unknown in "Baptornis" varneri); coracoid tubercle distal to glenoid (unknown in "Baptornis" varneri); humerus extremely slender (unknown in "Baptornis" varneri); short preacetabular process (unknown in "Baptornis" varneri); deep proximodorsal metatarsal III fossa; metatarsal IV trochlea >140% as wide as trochlea III; crescent and peg articulations between phalanges in pedal digit IV (unknown in "Baptornis" varneri).
Comments- This clade correlates to the Hesperornithidae of Martin (1984), which he supported with the cresecent and peg articulations in pedal digit IV.

Parahesperornis Martin, 1984
= "Parahesperornis" Martin, 1983
P. alexi Martin, 1984
= "Parahesperornis alexi" Martin, 1983
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Holotype- (KUVP 2287) (subadult) incomplete skull, mandible (208 mm), axis, first cervical vertebra, second cervical vertebra, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, incomplete sixth cervical vertebra, incomplete seventh cervical vertebra, incomplete eighth cervical vertebra, incomplete ninth cervical vertebra, incomplete tenth cervical vertebra, incomplete eleventh cervical vertebra, incomplete twelfth cervical vertebra, incomplete thirteenth cervical vertebra, incomplete fourteenth cervical vertebra, incomplete fifteenth cervical vertebra, incomplete sixteenth cervical vertebra, incomplete first dorsal vertebra, incomplete second dorsal vertebra, incomplete third dorsal vertebra, incomplete fourth dorsal vertebra, incomplete fifth dorsal vertebra, incomplete sixth dorsal vertebra, incomplete seventh dorsal vertebra, eighth dorsal vertebra, six partial dorsal ribs, two uncinate processes, synsacrum, first caudal centrum, incomplete coracoid, partial sternum, three sternal ribs, three partial sternal ribs, distal humerus, incomplete ilium, pubis, ischium, femur, patella, tibiotarsus, fibula, tarsometatarsus, phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, feathers, pedal scales (Williston, 1896)
Paratype- partial tarsometatarsus (Wetmore, unpublished MS)
Referred- (FHSM VP-17312) tarsometatarsus (97 mm) (Bell and Everhart, 2009)
(KUVP 24090) posterior mandible (Witmer, 1990)
(RMDRC coll.) pelvis (Anthony, pers. comm., 2009)
Other diagnoses- Lucas (1903) distinguished his Hargeria gracilis (based on the holotype of Parahesperornis) from Hesperornis regalis with two plesiomorphies- lacrimal ventral process slender; femur more elongate and less proximally expanded. Contra Lucas, the nasal processes do not appear shorter than H. regalis. While the orbital quadrate process is much longer than H. regalis specimen YPM 1206 as illustrated by Marsh, it is not much longer than the actual specimen of YPM 1206 or KUVP 71012, making this difference invalid.
Martin (1984) stated Parahesperornis' skull was mesokinetic (has a flexible frontoparietal joint), but this was later disproven by Buhler et al. (1988). Two of the characters listed by Martin are plesiomorphies compared to Hesperornis regalis- coracoid elongate; tarsometatarsal trochlea IV smaller and less projected distally. Contra Martin, the anterior lacrimal process is less extended anteriorly than in Hesperornis. Crescent and peg articulations on pedal digit IV are shared with Hesperornis. The tibiotarsus is said to be less compressed than Hesperornis, but without knowing the plane of depression this is vague.
Comments- The holotype was discovered in 1894 and referred to Hesperornis gracilis by Williston (1896, 1898). Lucas (1903) described it as an example of Hesperornis gracilis, using it to separate the species as Hargeria gracilis. However, the ICZN dictates Hargeria must stay associated with its type species regardless of what specimen its description was based on. The mandible was illustrated by Gregory (1951, 1952) as Hesperornis gracilis and Swinton (1975) as H. regalis, while a tooth was illustrated by Martin et al. (1980) as "a hesperornithid." Gregory (1951) argued the differences between regalis and KUVP 2287 were insufficient for generic separation, partially caused by inaccuracies in Marsh's illustrations. In 1952, he argued the quadrate was not disimilar when compared to the actual material instead of Marsh's illustration and that femoral differences could be caused by crushing. Gingerich (1973) described the skull and stated gracilis only differs from regalis in being slightly smaller, while in 1976 he deferred identification of KUVP 2287 to the species. Martin (1983) proposed the new taxon Parahesperornis alexi for KUVP 2287, but as Neas and Jenkinson (1986) note, it is not a proper description as it lacks a diagnosis (ICZN Article 13.1.1). The name is thus a nomen nudum until Martin's (1984) official description. While Martin (1984) states he has a full description in preparation, this has yet to appear. Some cranial morphologies were described by Buhler et al. (1988) and Witmer (1990). Both Witmer and Elzanowski (1991) have noted various unfused cranial sutures suggest it was not an adult.
Martin (1984) mentions a partial tarsometatarsus of Parahesperornis which was going to be described by Wetmore, but the paper was never completed.
Bell and Everhart (2009) described a tarsometatarsus as Parahesperornis sp., which is slightly more elongate with a smaller trochlea III (about half the size of IV).
References- Williston, 1896. On the dermal covering of Hesperornis. Kansas University Quarterly. 5(1), 53-54.
Williston, 1898. Birds. The University Geological Survey of Kansas, Part 2. 4, 43-53.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Gregory, 1951. Convergent evolution: The jaws of Hesperornis and the mosasaurs. Evolution. 5, 345-354.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Gingerich, 1973. Skull of Hesperornis and early evolution of birds. Nature. 243, 70-73.
Swinton, 1975. Fossil Birds. 3rd Ed. British Museum (Natural History), London. 1-81.
Gingerich, 1976. Evolutionary significance of the Mesozoic toothed birds. Smithsonian Contributions to Paleobiology. 27, 23-34.
Martin, Stewart and Whetstone, 1980. The origin of birds: structure of the tarsus and teeth. The Auk. 97, 86-93.
Martin, 1983. The origin and early radiation of birds. in Bush and Clark (eds). Perspectives in Ornithology. Cambridge University Press, Cambridge. 291-338.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Neas and Jenkinson, 1986. Type and figured specimens of fossil vertebrates in the collection of the University of Kansas Museum of Natural History, Part III. Fossil birds. Miscellaneous Publication 78, Museum of Natural History, University of Kansas, Lawrence. 1-14.
Bühler, Martin and Witmer, 1988. Cranial kinesis in the Late Cretaceous birds Hesperornis and Parahesperornis. The Auk. 105, 111-122.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Elzanowski, 1991. New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region. Postilla. 207, 20 pp.
Martin and Stewart, 1999. Implantation and replacement of bird teeth. Smithsonian Contributions to Paleobiology. 89, 295-300.
Bell and Everhart, 2009. A new specimen of Parahesperornis (Aves: Hesperornithiformes) from the Smoky Hill Chalk (Early Campanian) of Western Kansas. Transactions of the Kansas Academy of Science. 112(1/2), 7-14.

Hesperornis? mengeli Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, Manitoba, Canada

Holotype- (BO 780106) tarsometatarsus (85.6 mm)
Other diagnoses- Martin and Lim (2002) diagnosed this based on its small size, which is probably primitive and still larger than Hesperornis? macdonaldi. The more slender shaft is also plesiomorphic. Trochlea III is not smaller compared to IV than in Hesperornis crassipes and H. rossicus. Trochlea II is more hidden behind III in H. crassipes, H. rossicus and H. bazhanovi.
Comments- This was described as a species of Hesperornis, but its true position is more uncertain. The slender tarsometatarsus is more primitive than the Baptornis + Hesperornis clade, while the small size is unlike hesperornithids. However, the deep proximodorsal metatarsal III fossa and enlarged metatarsal IV trochlea are shared with the Parahesperornis + Hesperornis clade. The distally projecting metatarsal IV is like Hesperornis, but the rounded intercotylar process is not. The slender tarsometatarsus and medial cotyla which is not transversely compressed suggests it is not part of the large Hesperornis clade. It is here tentatively assigned to the Parahesperornis + Hesperornis clade, where it may be an extremely basal species of Hesperornis.
Reference- Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.

Canadaga Hou, 1999
C. arctica Hou, 1999
Middle Maastrichtian, Late Cretaceous
Bylot Island, Nunavut, Canada
Holotype
- (NMC 41050) incomplete fifteenth cervical vertebra, sixteenth cervical vertebra (28 mm), partial seventeenth cervical vertebra
Paratypes- ?(NMC 41053) (juvenile) femoral shaft
?(NMC 41054) (juvenile) femoral shaft
?(NMC 41064) (juvenile) last synsacral vertebra (29 mm)
Late Cretaceous
Devon Island, Nunavut, Canada
Referred
- sixteenth cervical vertebra, seventeenth cervical vertebra, first dorsal vertebra, rib fragments (Wilson et al., 2009)
Diagnosis- (after Hou, 1999) posterior cervical centrum expanded transversely to be wider than interzygapophyseal width; lateral fossa occupies entire posterior cervical centrum; large hypapophysis, extending from anterior rim to middle of centrum; angle between posterior cervical postzygapophyses much less than 90 degrees; short posterior cervical neural spines; well developed anterior ligament fossa on posterior cervical vertebrae.
(after Wilson et al., 2009) fovea between the parapophysis and centrum with a deep cavity below the transverse process.
Comments- Hou studied these remains in 1991 and described them in 1999 as a new taxon of hesperornithid- Canadaga arctica. While the diagnosis does distinguish Canadaga from Baptornis advenus and Hesperornis regalis, the remains of other hesperornithines are either not comparable or not described/illustrated well enough to compare. The size (estimated tarsometatarsal length of 212 mm) is greater than other hesperornithids, which suggests it may be referrable to the subgroup of large Hesperornis species. However, no other characters are presently known which could resolve where Canadaga belongs within Hesperornithes.
References- Hou, 1999. New hesperornithid (Aves) from the Canadian Arctic. Vertebrata PalAsiatica. 37(7), 228-233.
Wilson, Chin, Dyke and Cumbaa, 2009. A high-latitude hesperornithiform (Aves) from Devon Island: Paleobiogeography and size distribution of North American hesperornithiforms. Journal of Vertebrate Paleontology. 29(3), 202A.

Hesperornis Marsh, 1872a
= Lestornis Marsh, 1876
= Coniornis Marsh, 1893
= Hargeria Lucas, 1903
= Asiahesperornis Nessov and Prizemlin, 1991
Diagnosis- (proposed) hypertrophied ilial antitrochanter (also in Baptornis advenus); acetabulum partially closed (also in Baptornis advenus); pointed intercotylar process on tarsometatarsus (absent in Hesperornis crassipes); metatarsal IV extends distally far beyond III (also in Enaliornis? seeleyi).
Comments- While numerous species and specimens have been referred to Hesperornis, several have been given their own genera. Currently, the literature synonymizes Lestornis, Coniornis and Hargeria with Hesperornis, but retains Asiahesperornis as a separate genus. Yet no reasons for excluding the latter taxon from Hesperornis have been given, and it clades within Hesperornis when included in a phylogenetic analysis (unpublished). An alternative taxonomic decision would be to split Hesperornis into several genera, though this would require new genus names for at least H. bairdi and H? mengeli, while Lestornis could be used for the (crassipes + rossicus + bazhanovi) clade or else rossicus could get its own genus as well. Hesperornis mengeli and H. macdonaldi were named by Martin and Lim (2002), but are here provisionally removed from the genus.
References- Marsh, 1872a. Discovery of a remarkable fossil bird. American Journal of Science, Series 3. 3(13), 56-57.
Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Marsh, 1893. A new Cretaceous bird allied to Hesperornis. American Journal of Science. 45, 81-82.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107 (in Russian).
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.
Wilson, 2012. The effects of climate and behavior on avian bone microstructure: A comparative osteohistology study of hesperornithiforms from the Late Cretaceous Western Interior Seaway. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 195.
H. bairdi Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US

Holotype- (PU 17208A) synsacrum, incomplete ilium, proximal pubis, proximal ischium, tarsometatarsus (102.4 mm)
Other diagnoses- Martin and Lim (2002) diagnosed this based on Hesperornis characters (more enlarged and distally placed trochlea IV than Parahesperornis) and its primitively small size (which is still larger than H? mengeli and H? macdonaldi).
Comments- This taxon seems to be the most basal species of Hesperornis, which explains its similarity to Parahesperornis.
Reference- Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.
unnamed clade (Hesperornis regalis <- Hesperornis bairdi)
Diagnosis- (proposed) large size (proximal tarsometatarsal width over 25 mm); coracoid short proximodistally (unknown in H. bairdi); clavicles unfused (unknown in other hesperornithines); interclavicular angle >70 degrees (unknown in other hesperornithines); distal tibiotarsus not angled anteriorly (unknown in H. bairdi); tarsometatarsus robust (less than 4.5 times longer than proximally wide (also in "Baptornis" varneri); medial tarsometatarsal cotyla transversely compressed (also in Enaliornis? seeleyi).
Comments- This large Hesperornis clade may also include Canadaga, based on its size.
H. altus (Marsh, 1893) Shufeldt, 1915b
= Coniornis altus Marsh, 1893
Campanian, Late Cretaceous
Claggett Shale or Judith River Formation, Montana, US
Holotype
- (YPM 515) (adult) distal tibiotarsus
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, South Dakota, US

Referred- ?(YPM PU 17208) (YPM online)
?(YPM PU 17208a) (YPM online)
?(YPM PU 18589) (YPM online)
Diagnosis- indeterminate relative to H. regalis.
Comments- This specimen was discovered in 1892 and described by Marsh (1893) as a new taxon of hesperornithine, which he named Coniornis altus. This was based on two characters- lateral condyle projects distally further than medial condyle; medial condyle does not extend medially past shaft. Shufeldt (1915a) believed Marsh only separated Coniornis from Hesperornis on stratigraphic grounds, though he did not officially place altus in Hesperornis. Shufeldt (1915b) compared the element to Hesperornis regalis and found them similar enough to place in the same genus, or even the same species. He noted "where the condylar crests are more prominent in Hesperornis, they have been broken off in Marsh's Coniornis altus." He thus synonymized Coniornis with Hesperornis, which was followed by Martin (1984) due to the compressed distal end. Indeed, comparing the holotype to H. regalis, the two characters described by Marsh could be eliminated by rotating the distal end of altus' tibiotarsus so that the condyles are vertical instead of medially tilted. There is an obvious plaster filled area just proximal to the condyles where misalignment could have taken place. Once this is corrected for, the tibiotarsi are extremely similar. YPM 515 seems to have a more anteriorly projected lateral condyle, but this would again be solved by rotating the distal area. The lack of a medial epicondyle on YPM 515 could be due to damage.
Shufeldt (1915a) described Hesperornis montana from a dorsal vertebra found in the Claggett Shale of Montana and considered the possibility YPM 515 was from the same beds (as the area was not well segregated when it was collected), but felt it more likely that the size difference indicated there were two species present. They are here kept separate as many formations have more than one hesperornithid species, and there is no overlapping material. The referred material from the Pierre Shale Group may be H. bairdi, H. chowi, H? macdonaldi or H? mengeli based on stratigraphy.
References- Marsh, 1893. A new Cretaceous bird allied to Hesperornis. American Journal of Science. 45, 81-82.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Shufeldt, 1915b. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
H. montanus Schufeldt, 1915a
Early Campanian, Late Cretaceous
Claggett Shale, Montana, US

Holotype- (USNM 8199) sixth dorsal vertebra (Shufeldt, 1915a)
Diagnosis- (after Shufeldt, 1915a) lateral fossae extremely shallow in dorsal centra.
Comments- Shufeldt (1915) reported on a dorsal vertebra discovered in 1914, which he sent to Lull for examination. Lull determined it most closely matched the last dorsal vertebra of Hesperornis, differing only in minor ways, most of which also varied between different spcimens of that genus. He concluded it was referrable to Hesperornis, and only perhaps a new species due to stratigraphy. Shufeldt noted it may have been found in the same beds as Coniornis altus but thought it was too small to derive from the same species, so named it Hesperornis montana. However, the ICZN dictates it must be emmended to montanus, as Hesperornis is masculine.
Marsh (1893) earlier described Coniornis altus from what may be the same beds and while Shufeldt considered the possibility of synonymy (as have later authors), he felt it more likely that the size difference indicated there were two species present. They are here kept separate as many formations have more than one hesperornithid species, and there is no overlapping material.
References- Marsh, 1893. A new Cretaceous bird allied to Hesperornis. American Journal of Science. 45, 81-82.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
H. gracilis Marsh, 1876
= Hargeria gracilis (Marsh, 1976) Lucas, 1903
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Holotype- (YPM 1473) incomplete tarsometatarsus (~130 mm)
Referred- ?(YPM 1478) tarsometatarsi (one partial; 138 mm), phalanx IV-1 (41 mm) (Marsh, 1880)
?(YPM 1679) incomplete skeleton (Marsh, 1880)
Other diagnoses- Marsh (1876) diagnosed H. gracilis as being smaller and more slender than H. regalis, but these are plesiomorphies.
Comments- Martin (1984) incorrectly listed the holotype as YPM 1478 in his figure 1, which is a specimen listed in two tables as H. gracilis by Marsh (1880). The holotype was discovered in 1876 and briefly described by Marsh that year, but it was not illustrated until Martin (1984). Williston (1896, 1898) referred KUVP 2287 to Hesperornis gracilis, but it was later made the holotype of Parahesperornis alexi by Martin (1984). Lucas (1903) also believed KUVP 2287 was referrable to gracilis and used it as the basis for transferring that species to his new genus Hargeria. However, the ICZN dictates Hargeria must stay associated with its type species regardless of what specimen its description was based on. Lang (1973) placed a species of leptocheliid tanaidacean Leptochelia rapax Harger, 1879 into the new genus Hargeria. Thus the crustacean Hargeria is preoccupied by the bird Hargeria, contra Bell and Everhart (2009). Martin (1984) synonymized Hargeria with Hesperornis, but retained gracilis as a distinct species. The taxon needs to be described in detail to determine how it compares to other Hesperornis species.
YPM 1679 was referred to H. gracilis by Marsh (1880), but only listed as Hesperornis sp. by Chiappe (2002) and the YPM catalog.
References- Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Harger, 1879. Notes on New England Isopoda. Proceedings of the United States National Museum. 79, 157-165.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Lang, 1973. Taxonomische und phylogenetische Untersuchungen uber die Tanaidaceen (Crustacea). 8. Die Gattungen Leptochelia Dana, Heterotanais G.O. Sars und Nototanais Richardson. Dazu einige Bemerkungen uber die Monokonophora und ein Nachtrag. Zoologica Scripta. 2, 197-229.
Martin, Stewart and Whetstone, 1980. The origin of birds: structure of the tarsus and teeth. The Auk. 97, 86-93.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Bell and Everhart, 2009. A new specimen of Parahesperornis (Aves: Hesperornithiformes) from the Smoky Hill Chalk (Early Campanian) of Western Kansas. Transactions of the Kansas Academy of Science. 112(1/2), 7-14.
H. chowi Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US

Holotype- (PU 17208) tarsometatarsus (137.5 mm)
Diagnosis- (after Martin and Lim, 2002) medial anterior metatarsal ridge blends into median groove distally.
Other diagnoses- Martin and Lim (2002) disgnosed Hesperornis chowi with several characters that differ from H. regalis. However, the more elongate tarsometatarsus and slender lateral anterior metatarsal ridge are plesiomorphic, while the fourth trochlea is not more enlarged compared to trochlea III. A short medial anterior metatarsal ridge is also present in Hesperornis mengeli and H. bazhanovi.
Comments- Martin and Lim (2002) also believed remains described by Russell (1967) as H. regalis from the Northwest Territories might be H. chowi, but these are from a different formation.
References- Russell, 1967. Cretaceous vertebrates from the Anderson River, N.W.T. Canadian Journal of Earth Sciences. 4, 21-38.
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.
H. regalis Marsh, 1872a
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Holotype
- (YPM 1200) third cervical vertebra (22.5 mm), sixth cervical vertebra (29 mm), fourth dorsal vertebra (24 mm), fifth dorsal vertebra (24 mm), dorsal ribs, third caudal vertebra (12 mm), fourth caudal vertebra (12 mm), fifth caudal vertebra (13 mm), sixth caudal vertebra (13.5 mm), seventh caudal vertebra (13 mm), eighth caudal vertebra (15.2 mm), ninth caudal vertebra (16 mm), pygostyle (25 mm), partial pelvis, femora (89, 90 mm), tibiotarsi (320 mm), fibula (240 mm), tarsometatarsi (136 mm), phalanx III-1 (41 mm), phalanx III-2 (30 mm), proximal phalanx III-3, phalanx IV-1 (44 mm), phalanx IV-2 (39.5 mm), phalanx IV-3 (40 mm), proximal phalanx IV-4
Referred- (AMNH 2181) femur, tibiotarsus, fibula (AMNH online)
(AMNH 5100) sixteen cervical vertebrae, six dorsal vertebrae, synsacrum, four caudal vertebrae, scapulae, ilia, pubes, ischia, femora, patellae, tibiotarsi, fibulae, phalanx I-1, pedal ungual I, tarsometatarsi, phalanges II-1, phalanges II-2, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV (Sternberg, 1917)
(FMNH PA206) (Chiappe, 1996)
(FMNH PA316) (Chiappe, 1996)
(FSHM 186) fifth dorsal vertebra, sixth dorsal vertebra, synsacrum, incomplete ilium, proximal pubis (Oceans of Kansas)
(FHSM 2069) cervical vertebrae, dorsal vertebrae, dorsal ribs, synsacrum, caudal vertebrae, scapula, coracoids, incomplete sternum, sternal ribs, humerus, ilium, pubis, ischium, femur, patella, tibiotarsus, ribula, tarsometatarsus, proximal phalanx II-1, phalanx III-1, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4 (Oceans of Kansas)
(FHSM VP-2293) seven dorsal vertebrae, two proximal dorsal ribs, scapula, humerus (Oceans of Kansas)
(KUVP 2289) femoral fragment (Chinsamy, Martin and Dodson, 1998)
(KUVP 71012) skull, mandibles, tarsometatarsus (128 mm) (Martin, 1987; Witmer and Martin, 1987)
(KUVP 123108) distal femoral fragment (Chinsamy, Martin and Dodson, 1998)
(LACM 128317) maxilla (Witmer, 1990)
(UNSM 1212) fifteen presacral vertebrae, three dorsal ribs, uncinate processes, pubis, femur, patella, tarsometatarsus, phalanx III-1 (Oceans of Kansas)
(USNM 53) three vertebrae (USNM online)
(USNM 54) three vertebrae (USNM online)
(USNM 55) two vertebrae (USNM online)
(USNM 77) pelvis (USNM online)
(USNM 78) sternum (USNM online)
(USNM 4978) anterior skull, partial mandibles, eight cervical vertebrae, six dorsal vertebrae, dorsal ribs, partial uncinate process, synsacrum, caudal vertebrae, scapula, coracoid, clavicle, sternum, sternal ribs, ilium, pubis, ischium, femora, tibiotarsi, tarsometatarsi, pedal phalanges (Lucas, 1903)
(USNM 6622) premaxilla (USNM online)
(USNM 7276) partial mandible (USNM online)
(USNM 7277) partial mandible (USNM online)
(USNM 11640) vertebra, pelvis (USNM online)
(USNM 13580) dorsal vertebrae, dorsal rib, synsacrum, femur, patella, tibiotarsus, fibula, tarsometatarsus (Bryant, 1983)
(USNM 13581) femur, partial tibiotarsus, proximal tarsometatarsus, phalanx (USNM online)
(USNM 13882) dorsal vertebra (USNM online)
(YPM 903) posterior mandible (Shufeldt, 1915b)
(YPM 1201) partial femur (Marsh, 1872b)
(YPM 1202) partial femur (Marsh, 1872b)
(YPM 1203) phalanx (Marsh, 1872b)
(YPM 1204) (Marsh, 1872b)
(YPM 1205) distal tibiotarsus (Marsh, 1875)
(YPM 1206) skull (257 mm), mandible (257 mm), teeth, third cervical vertebra (24 mm), fourth cervical vertebra (26 mm), fifth cervical vertebra (28 mm), sixth cervical vertebra (31 mm), seventh cervical vertebra (32 mm), eighth cervical vertebra (33 mm), ninth cervical vertebra (32.5 mm), tenth cervical vertebra (32 mm), three cervicals ribs (37, 83 mm), fourth dorsal vertebra, sixth dorsal vertebra (25.5 mm), six dorsal ribs (145, 172, 190, 209 mm), six uncinate processes (25, 54, 52, 55, 50, 30 mm), synsacrum (320 mm- first sacral 21 mm), first caudal vertebra (19 mm), second caudal vertebra (15 mm), scapula, coracoid (54 mm), clavicle (78 mm), sternum (~200 mm), five incomplete sternal ribs (110 mm), humerus (152 mm), ilium (380 mm), pubis (330 mm), ischium (260 mm), femur (96 mm), tarsometatarsus (132 mm), proximal phalanx II-1, phalanx IV-1 (42.5 mm), phalanx IV-2 (40 mm), phalanx IV-3 (41 mm) (Marsh, 1875)
(YPM 1207) quadrate, occiput, axis (29 mm), third cervical vertebra (22 mm), fourth cervical vertebra (24 mm), fifth cervical vertebra (28 mm), sixth cervical vertebra (30 mm), seventh cervical vertebra (32 mm), eighth cervical vertebra (33 mm), ninth cervical vertebra (31 mm), tenth cervical vertebra (30 mm), eleventh cervical vertebra (29 mm), twelfth cervical vertebra (24 mm), thirteenth cervical vertebra (25 mm), fourteenth cervical vertebra (23 mm), fifteenth cervical vertebra (22 mm), sixteenth cervical vertebra (18 mm), seventeenth cervical vertebra (20 mm), first dorsal vertebra (22 mm), second dorsal vertebra (24 mm), third dorsal vertebra (24.5 mm), fourth dorsal vertebra (25 mm), fifth dorsal vertebra (24.5 mm), sixth dorsal vertebra (24 mm), coracoid (55 mm), partial clavicle, femora (98.5, 101 mm), patella (98 mm), tarsometatarsi (one partial; 136 mm) (Marsh, 1880)
(YPM 1470) synsacrum, caudal vertebra (YPM online)
(YPM 1471) limb bone fragments (YPM online)
(YPM 1472) femoral fragments (Marsh, 1880)
(YPM 1476) fourteenth cervical vertebra (24 mm), fifteenth cervical vertebra (22 mm), sixteenth cervical vertebra (18 mm), seventeenth cervical vertebra (22 mm), first dorsal vertebra (25 mm), second dorsal vertebra (26.5 mm), third dorsal vertebra (26 mm), fourth dorsal vertebra (26 mm), fifth dorsal vertebra (26 mm), scapula (135 mm), femur (105 mm), patella (100 mm), tibiotarsi (335, 325 mm), proximal fibula, metatarsal I (20 mm), distal phalanx I-1, pedal ungual I (14 mm), tarsometatarsi (136 mm), phalanx II-1 (42 mm), phalanx II-2 (41 mm), pedal ungual II (15 mm) (Marsh, 1880)
(YPM 1477) fourteenth cervical vertebra (24 mm), fifteenth cervical vertebra (22 mm), sixteenth cervical vertebra (19 mm), seventeenth cervical vertebra (20 mm), first dorsal vertebra (22 mm), second dorsal vertebra (24 mm), fourth dorsal vertebra (25 mm), fifth dorsal vertebra (26 mm), sixth dorsal vertebra (25 mm), seventh dorsal vertebra (22 mm), synsacrum, femur (97 mm), patella (103 mm), proximal fibula (Marsh, 1880)
(YPM 1491) femoral fragments, tibiotrarsus, tarsometatarsus (Chiappe, 1996)
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, South Dakota, US

(SDSM 25005) incomplete femur, tibiotarsus (315 mm), incomplete fibula (Martin and Varner, 1992)
Diagnosis- (after Marsh, 1875a, b) seventh through tenth caudal vertebrae with extremely long and flattened transverse processes (unknown in other hesperornithids); pygostyle extremely broad and flattened (unknown in other hesperornithids).
(after Marsh, 1876) four sternal rib articulations; deep posterolateral excavations in sternum.
(after Marsh, 1877) radius, ulna and manus absent (unknown in other hesperornithids).
(after Lucas, 1903) fourteen sacral vertebrae (unknown in other hesperornithids; also in Aves).
(after Witmer, 1990) medial pneumatic lacrimal fossa small and shallow (unknown in other Hesperornis); articular lacks pneumaticity (unknown in other Hesperornis; also in Patagopteryx).
(proposed) scapular expanded distally (unknown in other hesperornithines; also in Songlingornis); humerus longer than scapula (unknown in other hesperornithines; also in Gansus and Yanornis);
Other diagnoses- Marsh's (1872a) original paper only described a few characters, which are either more broadly distributed among hesperornithines (short femur, elongate tibiotarsus) or incorrect (unfused metatarsals).
Marsh's (1872b) later description mentions several features as being distinctive, but these are either primitive (trochanteric crest less expanded anteroposteriorly than in grebes; supratendinal groove absent; hypotarsal grooves absent) or found in other hesperornithines (femur with compressed cross section; metatarsal IV longest; trochlea IV enlarged; pedal digit IV with crescent and peg articulations between phalanges).
Marsh (1875a, b) mentions several characters as being distinctive, though the described proximal caudal morphology (short centra, moderate sized transverse processes and tall neural spines) is primitive. The partially closed acetabulum is present in some other hesperornithines as well.
In 1877, Marsh noted Hesperornis was also distinctive for having dentary teeth placed in grooves (also in Parahesperornis), a sternum without a keel (probably also in Baptornis), and a hindlimb with diving adaptations (too vague, and found in other hesperornithines in any case).
Lucas (1903a) noted the femur was articulated so that it projected transversely, which is also now known to be true in Parahesperornis.
Comments- The holotype was discovered in 1871, though another specimen (YPM 1205) was discovered in 1870 but not recognized as such until Marsh (1875a, b). Marsh (1872a) gave a very brief commentary on the holotype, to be followed by a more detailed description in 1872b. Marsh (1875a, b) added details from a more complete specimen with a skull (YPM 1206). Marsh (1880) monographed the taxon, using the holotype, YPM 1206, 1207, 1476 and 1477. He misidentified the predentary as a basihyal (Martin and Naples, 2008). Palatal elements have been controversial- a structure was identified by Marsh (1880) as a vomer, Gingerich (1973, 1976) as a palatine, and Elzanowski (1991) as an anterior pterygoid. Another element was identified as a palatine by Marsh, a vomer by Gingerich, and a composite maxilla and palatine fragment by Elzanowski. Witmer and Martin (1987) identified elements as a paired vomer which Elzanowski identified as palatines. Bock (1969) questioned whether Hesperornis was really toothed, but their presence in its jaws is unambiguous. Although the YPM lists YPM 1201-1204 as paratypes, Marsh 1872a only mentions one specimen in his initial description. These are probably the four specimens mentioned in Marsh 1872b. Note Gregory (1951) incorrectly called YPM 1206 the type.
Several specimens from other formations have been referred to Hesperornis. Russell (1967) mentioned many specimens from the Smoking Hills Formation of the Northwest Territories. Bardack (1968) referred numerous specimens from the Vermillion River Formation of Manitoba to H. regalis. These two records are difficult to evaulate without descriptions, though Witmer (1990) noted differences in some Vermillion River material. Fox (1974) referred a tarsometatarsus from the Foremost Formation of Alberta to Hesperornis cf. regalis, though this seems untrue based on its proportions.
References- Marsh, 1872a. Discovery of a remarkable fossil bird. American Journal of Science, Series 3. 3(13), 56-57.
Marsh, 1872b. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3(17), 359-365.
Marsh, 1873. Fossil birds from the Cretaceous of North America. American Journal of Science, Series 3. 5(27), 229-231.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Marsh, 1877. Characters of the Odontornithes, with notice of a new allied genus. American Journal of Science. 14, 85-87.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Noack, 1880. Die Bedeutung des Hesperornis regalis für die Descendanzteorie. Jahresber. Ver. Naturwiss. Braunschweig. 1, 89-96.
Marsh, 1883. Birds with teeth. 3rd Annual Report of the Secretary of the Interior. 3, 43-88.
Thompson, 1890. On the systematic position of Hesperornis. Studies from the Museum of Zoology. 1(10), 15 pp.
Lucas, 1903a. A skeleton of Hesperornis. Smithsonian Miscellaneous Collections. 45, 95.
Lucas, 1903b. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Brown, 1911. Notes on the restorations of the Cretaceous birds Hesperornis and Baptornis. Annals of the New York Academy of Sciences. 20, 401.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Shufeldt, 1915b. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Shufeldt, 1915c. On a restoration of the base of the cranium of Hesperornis regalis. Bulletins of American Paleontology. 5, 73-85.
Sternberg, 1917. Hunting Dinosaurs in the Badlands of the Red Deer River, Alberta, Canada. Published by the author, San Diego, California. 261 pp.
Stolpe, 1935. Colymbus, Hesperornis, Podiceps: ein Vergleich ihrer hinteren Extremität. Journal of Ornithology. 83(1), 115-128.
Lane, 1947. A survey of the fossil vertebrates of Kansas, Part IV, The Birds. Kansas Academy of Science, Transactions. 49(4), 390-400.
Edinger, 1951. The brains of the Odontognathae. Evolution. 5(1), 6-24.
Gregory, 1951. Convergent evolution: The jaws of Hesperornis and the mosasaurs. Evolution. 5, 345-354.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Martin and Tate, 1966. A bird with teeth. Museum Notes, University of Nebraska State Museum. 29, 1-2.
Russell, 1967. Cretaceous vertebrates from the Anderson River, N.W.T. Canadian Journal of Earth Sciences. 4, 21-38.
Walker, 1967. Revival of interest in the toothed birds of Kansas. Kansas Academy of Science, Transactions. 70(1), 60-66.
Bardack, 1968. Fossil vertebrates from the marine Cretaceous of Manitoba. Canadian Journal of Earth Sciences. 5, 145-153.
Bock, 1969. The origin and radiation of birds. Ann. New York Acad. Sci. 167, 147-155.
Gingerich, 1973. Skull of Hesperornis and early evolution of birds. Nature. 243, 70-73.
Fox, 1974. A Middle Campanian, nonmarine occurrence of the Cretaceous toothed bird Hesperornis Marsh. Canadian Journal of Earth Sciences. 11(9), 1335-1338.
Gingerich, 1976. Evolutionary significance of the Mesozoic toothed birds. Smithsonian Contributions to Paleobiology. 27, 23-34.
Martin, 1980. Foot-propelled diving birds of the Mesozoic. Acta XVII Congress of International Ornithology. 1237-1242.
Martin, Stewart and Whetstone, 1980. The origin of birds: structure of the tarsus and teeth. The Auk. 97, 86-93.
Bryant, 1983. Hesperornis in Alaska. Paleobios. 40, 1-8.
Martin, 1983. The origin and early radiation of birds. in Bush and Clark (eds). Perspectives in Ornithology. Cambridge University Press, Cambridge. 291-338.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Buhler, 1987. On the mobility of the upper jaw and the segments of the braincase in the Mesozoic birds. in Mourer-Chauvire (ed). L'évolution des oiseaux d'après le témoignage des fossiles. Docum. Lab. Geol. Fac. Sci. Lyon. 99, 41-48.
Martin, 1987. The beginning of the modern avian radiation. in Mourer-Chauvire (ed). L'évolution des oiseaux d'après le témoignage des fossiles. Docum. Lab. Geol. Fac. Sci. Lyon. 99, 9-19.
Witmer and Martin, 1987. The primitive features of the avian palate, with special reference to Mesozoic birds. in Mourer-Chauvire (ed). L'évolution des oiseaux d'après le témoignage des fossiles. Docum. Lab. Geol. Fac. Sci. Lyon. 99, 21-40.
Bühler, Martin and Witmer, 1988. Cranial kinesis in the Late Cretaceous birds Hesperornis and Parahesperornis. The Auk. 105, 111-122.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Elzanowski, 1991. New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region. Postilla. 207, 20 pp.
Martin and Varner, 1992. The occurence of Hesperornis in the Late Cretaceous Niobrara Formation of South Dakota. Proceedings of the South Dakota Academy of Science. 71, 95-97.
Chiappe, 1996. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Chinsamy, Martin and Dodson, 1998. Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas. Cretaceous Research. 19(2), 225-233.
Everhart, 2000-2009. http://www.oceansofkansas.com/Hesperornis.html
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.
Naples and Martin, 2004. Mandibular kinesis in Hesperornis. Sixth International Meeting of the Society of Avian Paleontology and Evolution, Abstracts. 46.
Reynaud, 2005. Functional morphology of the hindlimbs of Hesperornis regalis: A comparison with modern diving birds. Geological Society of America Abstracts with Programs. 37(7), 133.
Reynaud, 2006. Hindlimb and pelvis proportions of Hesperornis regalis: A comparison with extant diving birds. Journal of Vertebrate Paleontology. 26(3), 115A.
Martin and Naples, 2008. Mandibular kinesis in Hesperornis. Oryctos. 7, 61-65.
Zinoviev, 2009. Notes on hindlimb myology and syndesmology of Hesperornis regalis (Aves: Hesperornithiformes). Journal of Vertebrate Paleontology. 29(3), 207A.
unnamed clade (Hesperornis bazhanovi + Hesperornis crassipes + Hesperornis rossicus)
Diagnosis (proposed) metatarsal II trochlea almost completely hidden in anterior view (also in Pasquiaornis and Enaliornis? sedgwicki).
H. crassipes (Marsh, 1876) Marsh, 1880
= Lestornis crassipes Marsh, 1876
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Holotype- (YPM 1474) partial skeleton including dentary fragment, anterior angular, teeth, atlantal centrum, fourth cervical vertebra (24 mm), coracoid, clavicle (~80 mm), sternum (196 mm), partial femur (103 mm), patella (109 mm), tarsometatarsi (135 mm), phalanx II-1 (40.5 mm), phalanx III-1 (39 mm), phalanx IV-1 (42 mm), phalanx IV-2 (38 mm)
Referred- ?(AMNH 5102) incomplete tarsometatarsus (Nessov and Yarkov, 1993)
Diagnosis- (after Marsh, 1876) shallow posterolateral excavation in sternum; large proximolateral rugosity on metatarsal II.
(proposed) coracoid articulations on sternum widely separated (unknown in other Hesperornis; also in Patagopteryx).
Other diagnoses- Marsh (1876) also noted the sternum had five rib articulations as opposed to H. regalis' four, but this is primitive as Baptornis and Ichthyornis also have five. The less excavated posterolateral sternal margin has uncertain polarity, as Ichthyornis' is also shallow, whereas Gansus' is very deep.
Contra Marsh (1880), the tarsometatarsus does not appear more robust than in H. regalis.
Comments- Discovered in 1876, the specimen described that year by Marsh as a new genus of hesperornithid. Marsh (1880) placed it in Hesperornis without comment, provided illustrations and further measurements. The angular is illustrated by Gregory (1952). The species was accepted as valid by Martin (1984), but it desperately needs to be redescribed. The tarsometatarsus as illustrated by Marsh is quite distinct in shape from other Hesperornis, but the taxon clades within Hesperornis when included in a phylogenetic analysis (unpublished).
References- Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
H. rossicus Nessov and Yarkov, 1993
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Rychkovo, Volgograd, Russia

Holotype- (VRM 26306/2) proximal tarsometatarsus (~173 mm)
Paratypes- (VRM 26306/2a) partial sixteenth cervical vertebra
(VRM 26306/26) pedal phalanx IV-3
(VRM 26306/3) distal tarsometatarsus
(VRM coll.) dorsal vertebral fragment
Referred- (PO 5099) (subadult) proximal tarsometatarsal fragment (Nessov and Yarkov, 1993)
? posterior dorsal vertebra, proximal tarsometatarsus (Yarkov and Nessov, 2000)
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Ivo Klack, Sweden
Paratype-
(RM PZ R398) proximal tarsometatarsus
Referred- ?(LO 9067t) distal tibiotarsus (Mourer-Chauvire, 1992)
(SGU 3442 Ve01) proximal tarsometatarsus (Rees and Lindgren, 2005)
?(SGU 3442 Ve02) fifth dorsal vertebra (32 mm) (Rees and Lindgren, 2005)
Early Campanian, Late Cretaceous
Rybushka Formation, Saratov, Russia

(PO 5463) distal tarsometatarsus (~167 mm) (Panteleev, Popov and Averianov, 2004)
(PO 5464) (subadult) incomplete tarsometatarsus (158.8 mm) (Panteleev, Popov and Averianov, 2004)
Early Maastrichtian(?), Late Cretaceous
Bereslavka, Vologograd, Russia

distal tarsometatarsal fragment (Yarkov and Nessov, 2000)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, Manitoba, Canada

? tibiotarsus and/or tarsometatarsus (Aotsuka et al., 2012)
Diagnosis- (after Nessov and Yarkov, 1993) adult size with tarsometarsus over 150 mm long (also in Canadaga).
(after Kurochkin, 2000) proximal end of tarsometatarsus over 160% wider than deep.
(after Panteleev et al., 2004) tarsometatarsal trochlea IV over 250% as wide as trochlea III in anterior view.
Other diagnoses- Kurochkin (2000) listed several diagnostic characters. The proximal tarsometatarsal articular surface is not more diagonally oriented than in H. crassipes or H. bairdi. The lateral edge of the lateral cotyla does not extend proximally past the intercotylar eminance, contra Kurochkin. He states the medial cotyla is located more distally than the lateral cotyla, which may be the same character as Rees and Lindgren's (2005) "cotyla medialis slopes distally in regard to the nearly horizontal plane formed by the cotyla lateralis." However, it seems Rees and Lindgren mistook their proximal metatarsus SGU 3442 Ve01 as a left element when it is in fact from the right side. Perhaps Kurochkin made the same mistake with the holotype, as the lateral condyle is more distally placed in all specimens, which is typical of hesperornithids.
Panteleev et al. (2004) noted the inner toes were reduced, and while it seems trochlea IV was indeed enlarged compared to III, the size of II is uncertain due to damage. The absence of a ginglymoid trochlea II and III is shared with Hesperornis mengeli, while trochlea II is equally hidden behind metatarsal III in H. bazhanovi and crassipes.
Rees and Limdgren (2005) listed a few additional diagnostic characters. They state the cotyla have less curvature, but this seems untrue of lateral cotyla at least, while the concavity of H. bazhanovi's medial cotyla does not seem very different. The intercotylar eminence does not seem more pointed than Hesperornis bazhanovi, H. chowi or H. bairdi.
Comments- This species was originally named H. rossica, but must be emended to rossicus as Hesperornis is masculine (Kurochkin, 2000). The holotype was first reported by Nessov (in Mourer-Chauvire, 1991) as "an advanced hesperornithiform." The two vertebral fragments and pedal phalanx were referred to H. rossicus by Nessov and Yarkov (1993), though Kurochkin and Rees and Lindgren (2005) felt this was problematic due to the presence of PO 5099. PO 5099 was originally referred to Hesperornis sp. by Nessov and Yarkov (1993), but determined to be a young specimen of H. rossicus by Panteleev et al. (2004). Thus only H. rossicus is known from that locality, which makes the referral of the vertebrae and phalanx more probable. Yarkov and Nessov (2000) referred a tarsometatarsal fragment reworked to Paleocene deposits at Bereslavka to Hesperornithidae indet., but Panteleev et al. (2004) referred it to H. rossicus. Yarkov and Nessov also described a proximal tarsometatarsus and dorsal vertebra as Hesperornis sp., which is tentaively referred to H. rossicus here, as it is from the same locality. Rees and Lindgren (1999, 2005) described a dorsal vertebra and partial tibiotarsus as Hesperornis sp., but these are here provisionally referred to H. rossicus due to the presence of only one known hesperornithid at that locality and their large size. LO 9067t had been previously mentioned as a possible large hesperornithine by Nessov (in Mourer-Chauvire, 1992).
References- Mourer-Chauvire, 1991. Society of Avian Paleontology and Evolution Information Newsletter. 5.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov, 1992. [Flightless birds of meridional Late Cretaceous sea straits of North America, Scandinavia, Russia and Kazakhstan as indicators of features of oceanic circulation.] Byulleten Moskovskogo Obshchestva Ispytatelet Prirody Otdel Geologicheskii. 67, 78-83.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Rees and Lindgren, 1999. Early Campanian hesperornithiform birds from the Kristianstad Basin, southern Sweden. in Hoch and Brantsen (eds). Secondary adaptation to life in water. Abstracts. University of Copenhagen, Copenhagen. 53.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Yarkov and Nessov, 2000. New remains of hesperornithiform birds Hesperornithiformes from the Volgograd Reigion. Russkii Ornitolocheskii Zhurnal, Ekspress Vypusk. 94, 3-12. [in Russian]
Panteleev, Popov and Averianov, 2004. New record of Hesperornis rossicus (Aves, Hesperornithiformes) in the Campanian of Saratov Province, Russia. Paleontological Research. 8(2), 115-122.
Rees and Lindgren, 2005. Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 48(6), 1321-1329.
Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in Southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.
H. bazhanovi (Nessov and Prizemlin, 1991) new combination
= Asiahesperornis bazhanovi Nessov and Prizemlin, 1991
Maastrichtian, Late Cretaceous
Zhuravlovskaya Svita (not Eginsaiskaya Svita), Kazakhstan

Holotype- (IZASK 5/287/86a) incomplete tarsometatarsus (~122 mm)
Paratypes- (IZASK 5/287/86) dorsal vertebra
(IZASK 5/287/86b) partial tarsometatarsus
(IZASK 5/287/86B) distal tibiotarsus
(IZASK 5/293/87) dorsal vertebra
Referred- (IZASK 1/KM 97) proximal tarsometatarsus (~120-125 mm) (Malakhov and Ustinov, 1998)
(IZASK 2/KM 97) cervical vertebra (Malakhov and Ustinov, 1998)
(IZASK 3/KM 97) partial tarsometatarsus (~80-90 mm) (Malakhov and Ustinov, 1998)
(IZASK 4/KM 97) incomplete dentary (Malakhov and Ustinov, 1998)
(IZASK 5/KM 97) distal femur (~60-70 mm) (Malakhov and Ustinov, 1998)
(IZASK 22/KM 97) tooth (Malakhov and Ustinov, 1998)
(IZASK 218/B-2003) partial tibiotarsus (Dyke et al., 2006)
(IZASK 220/B-2003) partial tarsometatarsus (Dyke et al., 2006)
? two distal tibiotarsi, proximal tarsometatarsus (Nessov in Mourer-Chauvire, 1992)
Diagnosis- (after Nessov and Prizemlin, 1991) (?) medial tibiotarsal condyle markedly compressed transversely; (?) anterior intercondylar groove deep; (?) scar for the attachment of the first metatarsal is very small, located proximally on the shaft.
(proposed) round fossa around distal vascular foramen between metatarsals III and IV.
Other diagnoses- Kurochkin (2000) listed the characters from Nessov and Prizemlin's (1991) diagnosis (which has not been translated from Russian) which he considered were not generalized hesperornithine characters. The gracility and parallel sides of the tarsometatarsus are plesiomorphies compared to Hesperornis regalis. The sharp posterolateral tarsometatarsal crest is also present in Hesperornis bairdi, while a sharp posteromedial crest is present in H. bairdi, H? mengeli and Parahesperornis. A deep proximodorsal metatarsal III fossa is also present in Hesperornis and Parahesperornis, while those of H. regalis and H. chowi are equally narrow. The high dorsolateral crest by this feature is not easily observable in the figures, so cannot be compared to other taxa. Hesperornis chowi and Parahesperornis also have an expanded fossa distally between metatarsals III and IV, though they are not as round as in Asiahesperornis. Trochlea IV is larger compared to III in Hesperornis crassipes, H? mengeli and H. rossicus than in bazhanovi. The remaining characters listed above aren't possible to see in the published figures, making comparison to other taxa and thus their diagnostic status uncertain. However, compressed medial tibiotarsal condyles and deep intercondylar grooves are present in most derived hesperornithines.
Dyke et al. (2006) listed a couple additional features in their diagnosis. Hesperornis and Parahesperornis also have prominent medial and lateral grooves on the dorsal tarsometatarsus between the metatarsals. Hesperornis regalis and H. bairdi both have well developed grooves on the posterior surface of their third trochlea.
Comments- The type material was first reported by Prizemlin and Nessov (in Mourer-Chauvire, 1990) as "a large hesperornithiform bird of a new genus, and maybe a new family." Nessov and Prizemlin (1991) later described it as the new genus Asiahesperornis, which they placed in a new subfamily Asiahesperornithinae. Yet comparisons suggest the species is more similar to Hesperornis regalis than some other species assigned to that genus such as H. bairdi and H? mengeli, where is is resolved in phylogenetic analyses (unpublished). Thus it is placed within Hesperornis here, in a combination not seen in the literature.
The stratigraphy of the Kushmurun Quarry where Asiahesperornis is found has been controversial, with Dyke et al. (2006) assigning it to the Zhuravlovskaya Svita, not the Eginsaiskaya Svita as found in Nessov in Mourer-Chauvire (1992) and Kurochkin (2000). IZASK 5/287/86 was originally misidentified as a cervical vertebra by Nessov and Prizemlin (1991), but reidentified by Kurochkin (2000). This material is only provisionally referred to a single taxon of hesperornithine, based on size. Nessov and Yarkov (1993) later illustrated IZASK 5/293/87 and 5/287/86B as merely "hesperornithiforms" and provisionally assigned IZASK 5/287/86b to another species, but Dyke et al. found no reason to doubt their assignment to Asiahesperornis.
References- Mourer-Chauvire, 1990. Society of Avian Paleontology and Evolution Information Newsletter. 4.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107 (in Russian).
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Malakhov and Ustinov, 1998. New findings of Upper Cretaceous toothed birds (Aves; Hesperornithiformes) in northern Kazakhstan. Kazakh State University Yearbook, Biological Series. 1998, 162-167 (in Russian).
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Dyke, Malakhov and Chiappe, 2006. The hesperornithiform bird Asiahesperornis from Kushmurun, Northern Kazakhstan. Journal of Vertebrate Paleontology. 26(3), 57A-58A.
Dyke, Malakhov and Chiappe, 2006. A re-analysis of the marine bird Asiahesperornis from northern Kazakhstan. Cretaceous Research. 27(6), 947-953.
H. sp. nov. (Aotsuka, Hatcher, Janzic and Sato, 2012)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, Manitoba, Canada

Material- tibiotarsus and/or tarsometatarsus
Diagnosis- (after Aotsuka et al., 2012) shaft strongly constricted at midshaft; proximal articulation displays nearly D-shaped outline.
Reference- Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in Southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.
H. sp. (Shufeldt, 1915a)
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US

Material- (USNM 244239) tarsometatarsus (USNM online)
(YPM 1475) (YPM online)
(YPM 1479) vertrbral fragments, sacral fragments (Chiappe, 2002)
(YPM 1480) proximal tibiotarsus, phalanx (Chiappe, 2002)
(YPM 1481) sacrum, femur, tibiotarsus, tarsometatarsus (Chiappe, 2002)
(YPM 1482) tibiotarsal fragment (YPM online)
(YPM 1483) vertebral fragments, synsacral fragments (YPM online)
(YPM 1484) synsacral fragments (YPM online)
(YPM 1485) vertebral fragment (YPM online)
(YPM 1486) proximal tarsometatarsal fragments (YPM online)
(YPM 1487) vertebral fragments, synsacral fragments (YPM online)
(YPM 1488) fragments (YPM online)
(YPM 1489) femur, tibiotarsus, fragments (Chiappe, 2002)
(YPM 1490) vertebral fragments, synsacrum (YPM online)
(YPM 1492) vertebral fragments (YPM online)
(YPM 1493) fragmentary synsacrum (YPM online)
(YPM 1494) fragments (YPM online)
(YPM 1495) vertebral fragment (YPM online)
(YPM 1496) synsacral fragment (YPM online)
(YPM 1497) skull, cervical vertebra(e), rib (YPM online)
(YPM 1498) phalanx (YPM online)
(YPM 1499) sixth dorsal vertebra (Shufeldt, 1915a)
Comments- Shufeldt (1915a) quoted Lull as saying YPM 1499 is either H. regalis or H. sp. indet., and is more similar to H. montanus than to H. regalis specimens YPM 1206, 1474 and 1477 in size, general appearence and the shallowness of its lateral central fossae. These specimens are listed by Chiappe (2002) and the YPM collections as being Hesperornis sp., and may be H. regalis, H. gracilis, H. crassipes or even Parahesperornis based on their locality.
References- Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
H. sp. (Macdonald, 1951)
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US

Material- partial skeletons
Comments- Nicholls and Russell (1990) listed sixty-five specimens of Hesperornis from this formation, though some are probably the types of H. bairdi, H. chowi, H. macdonaldi or H. mengeli.
Reference- Macdonald, 1951. The fossil Vertebrata of South Dakota. in Guidebook, Fifth Field Conference, Society of Vertebrate Paleontology. 63-74.
Nicholls and Russell, 1990. Paleobiogeography of the Cretaceous Western Interior Seaway of North America: the vertebrate evidence. Palaeogeography, Palaeoclimatology, Palaeoecology. 79, 149-169.
H. sp. (Martin and Tate, 1967)
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, Nebraska, US

Material- partial skeleton
Comments- This was discovered in 1966, and may be H. bairdi, H. chowi, H? macdonaldi or H? mengeli based on stratigraphy.
Reference- Martin and Tate, 1967. A Hesperornis from the Pierre Shale. Nebraska Academy of Science Proceedings. 77th Annual Meeting. 40.
H. cf. regalis (Russell, 1967)
Early Campanian, Late Cretaceous
Smoking Hills Formation, Northwest Territories, Canada

Material- (some juvenile) many specimens
Comments- Russell (1967) referred remains found in 1965 to Hesperornis regalis based mostly on size, but according to Martin and Lim these may H. chowi instead. However, the "brown beds" of the Anderson River are not from the same formation as H. chowi.
Reference- Russell, 1967. Cretaceous vertebrates from the Anderson River, N.W.T. Canadian Journal of Earth Sciences. 4, 21-38.
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing. 113-124.
H. sp. (Bardack, 1968)
Campanian, Late Cretaceous
Boyne Member of the Vermillion River Formation, Manitoba, Canada
Material
- (FMNH 219) braincase fragment, posterior mandible, seven incomplete dorsal vertebrae, femora, partial tibiotarsus, tarsometatarsus
Comments- These were collected in 1965 and referred to H. regalis by Bardack (1968). Witmer (1990) notes the postcranium is slightly more gracile and that differences exist in middle ear morphology, making that assignment uncertain. This is especially true with the recent description of other species similar to H. regalis, such as H. chowi.
References- Bardack, 1968. Fossil vertebrates from the marine Cretaceous of Manitoba. Canadian Journal of Earth Sciences. 5, 145-153.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
H. sp. (Bardack, 1968)
Campanian, Late Cretaceous
Pembina Member of the Vermillion River Formation, Manitoba, Canada
Material
- femur (Bardack, 1968)
(CFDC B.00.01.00) femur (91 mm) (CFDC online)
(CFDC B.00.02.00) femur (lost) (CFDC online)
(CFDC B.00.03.00) femur (95 mm) (CFDC online)
(CFDC B.00.04.00) femur (82.5 mm) (CFDC online)
(CFDC B.00.05.00) femur (87.5 mm) (CFDC online)
(CFDC B.00.06.00) femur (72 mm) (CFDC online)
(CFDC B.00.07.00) femur (lost) (CFDC online)
(CFDC B.00.08.00) distal femur (CFDC online)
(CFDC B.00.11.05) partial femur (CFDC online)
(CFDC B.00.12.05) two femoral fragments (CFDC online)
(CFDC B.00.13.00) femur (CFDC online)
169 specimens (Nicholls and Russell, 1990)
Comments- The femur was collected before 1935 and referred to H. regalis by Bardack (1968). Nicholls and Russell (1990) listed 170 specimens of Hesperornis from the Pembina Member. Referral to regalis must remain questionable given the diversity of recently discovered Hesperornis species.
References- Bardack, 1968. Fossil vertebrates from the marine Cretaceous of Manitoba. Canadian Journal of Earth Sciences. 5, 145-153.
Nicholls and Russell, 1990. Paleobiogeography of the Cretaceous Western Interior Seaway of North America: the vertebrate evidence. Palaeogeography, Palaeoclimatology, Palaeoecology. 79, 149-169.
H. sp. (Fox, 1974)
Late Campanian, Late Cretaceous
Foremost Formation, Alberta, Canada
Material
- (UA 9716) tarsometatarsus (147 mm) (Fox, 1974)
(UCMP 108074) tarsometatarsus (UCMP online)
Comments- UA 9716 was discovered in 1972 and described by Fox (1974) as Hesperornis cf. regalis. He noted it was more similar to regalis than to crassipes in being slender and lacking the metatarsal II tuberosity of crassipes, though it is slightly larger. However, the lack of a rugosity is plesiomorphic and the width / length ratio (4.47) resembles H. gracilis (4.45) more than H. regalis (4.00-4.13). The proximodorsal metatarsal III fossa seems larger than H. gracilis, though this may be due to photocopy quality in my copy. Nessov and Yarkov (1993) thought it possibly belonged to "another more advanced species."
References- Fox, 1974. A Middle Campanian, nonmarine occurrence of the Cretaceous toothed bird Hesperornis Marsh. Canadian Journal of Earth Sciences. 11(9), 1335-1338.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
H. sp. (Case, 1978)
Late Campanian, Late Cretaceous
Teapot Sandstone Member of the Mesaverde Formation, Wyoming, US
Material
- (YPM PU 22390) partial tarsometatarsus (Case, 1978)
(YPM PU 22406) sternal fragment, three femora, fragments (Case, 1978)
(YPM PU 22407) distal tibiotarsal fragment (Case, 1978)
(YPM PU 22408) distal tibiotarsal fragment (Case, 1978)
(YPM PU 22437) three vertebrae, synsacrum, two phalanges (Case, 1978)
(YPM PU 22438) distal metatarsal IV (Case, 1978)
(YPM PU 22443) vertebrae, limb elements including tibiotarsus (Houde, 1987)
(YPM PU 22948) frontal (YPM online)
(YPM PU 22949) articular (YPM online)
Comments- Houde (1987) reported on the histology of YPM PU 22443, calling it Hesperornis sp..
References- Case, 1978. News from members; Eastern region; Jersey City. Society of Vertebrate Paleontology. News Bulletin. 114, 16-17.
Houde, 1987. Histological evidence for the systematic position of Hesperornis (Odontornithes: Hesperornithiformes). The Auk. 104(1), 125-129.
H? sp. (Bryant, 1983)
Coniacian-Campanian, Late Cretaceous
Ignek Formation, Alaska, US
Material
- (UCMP 103841) (subadult) partial third dorsal vertebra, partial fourth dorsal vertebra, partial fifth dorsal vertebra
Comments- This specimen was discovered in 1962 and described by Bryant (1983) as Hesperornis sp.. He found no differences between it and H. regalis specimen USNM 13580, and thought differences from the H. regalis holotype were due to age. However, other hesperornithines are difficult to compare, so the generic assignment should be provisional.
Reference- Bryant, 1983. Hesperornis in Alaska. Paleobios. 40, 1-8.
H. sp. (Hills, Nicholls, Núñez-Betelu and McIntyre, 1999)
Campanian, Late Cretaceous
Kanguk Formation, Nunavut, Canada
Material
- distal tarsometatarsus
Reference- Hills, Nicholls, Núñez-Betelu and McIntyre, 1999. Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities. Canadian Journal of Earth Sciences. 36(9), 1583-1588.
H. sp. (Hills, Nicholls, Núñez-Betelu and McIntyre, 1999)
Late Campanian-Early Maastrichtian, Late Cretaceous
Mason River Formation, Northwest Territories, Canada
Reference
- Hills, Nicholls, Núñez-Betelu and McIntyre, 1999. Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities. Canadian Journal of Earth Sciences. 36(9), 1583-1588.
H. sp. (Tokaryk, 1999)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, Saskatchewan, Canada

Material- (Tokaryk, 1999)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, South Dakota, US
Material
- (UCMP 113168) femur, tibiotarsus, pedal phalanges (UCMP online)
(UCMP 113169) tarsometatarsus (UCMP online)
(UCMP 113170) vertebrae (UCMP online)
(UCMP 123257) vertebral fragments, patella, pedal phalanges (UCMP online)
(UCMP 123258) femur (UCMP online)
(UCMP 123259) incomplete skeleton (UCMP online)
(USNM 244158) femur (USNM online)
(USNM 244159) proximal tibiotarsus, distal tibiotarsus (USNM online)
(USNM 244160) femur (USNM online)
(USNM 244161) tarsometatarsus (USNM online)
(USNM 244163) femur (USNM online)
(YPM 17193) (YPM online)
Comments- These may be H. bairdi, H. chowi, H? macdonaldi or H? mengeli based on stratigraphy.
Reference- Tokaryk, 1999. The toothed bird Hesperornis sp. (Hesperornithiformes) from the Pierre Shale (Late Cretaceous) of Saskatchewan. The Canadian Field-Naturalist. 113(4), 670-672.
H? sp. (Yarkov and Nessov, 2000)
Early Maastrichtian(?), Late Cretaceous
Bereslavka, Vologograd, Russia

Material- mid dorsal centrum, posterior dorsal centrum, pedal phalanx IV-?
Comments- Yarkov and Nessov (2000) referred two dorsal centra and a pedal phalanx to Hesperornithidae indet.
Reference- Yarkov and Nessov, 2000. New remains of hesperornithiform birds Hesperornithiformes from the Volgograd Reigion. Russkii Ornitolocheskii Zhurnal, Ekspress Vypusk. 94, 3-12. [in Russian]
H? sp. (Hutchinson, 2001)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US
Material
- (MOR 971) tarsometatarsus (MOR online)
(MOR 975) distal tarsometatarsus (MOR online)
(UCMP 130124) proximal femur (Hutchinson, 2001)
(UCMP 131164) femur (Hutchinson, 2001)
Comments- The UCMP specimens are referred to cf. Hesperornis by Hutchinson (2001), while the MOR specimens are referred to Hesperornis in the museum's collection. The stratigraphic position suggests comparison to Potamornis, though without a description any identification must remain uncertain.
Reference- Hutchinson, 2001. The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnaean Society. 131, 169-197.
H? sp. (Hilton, 2003)
Campanian, Late Cretaceous
Chico Formation, California, US

Material- (SC-VBHEi) pedal phalanx
Reference- Hilton, 2003. Dinosaurs and other Mesozoic reptiles of California. Aves. California University Press. 74-77.
H. sp. nov. (Kurochkin, 2004)
Early Campanian, Late Cretaceous
Rybushka Formation, Saratov, Russia

Material- proximal tarsometatarsus (40.4 mm wide)
Comments- Kurochkin (2004) stated this differs from the contemporary H. rossicus "by inverse ratio of the articular cotylas and some other characters", and that it also differs from H. regalis, H. crassipes, H. gracilis and H. bairdi, so is a new species.
Reference- Kurochkin, 2004. New fossil birds from the Cretaceous of Russia. Sixth International Meeting of the Society of Avian Paleontology and Evolution, Abstracts. 35-36.
H. sp. (UCMP online)
Late Cammpanian, Late Cretaceous
Judith River Formation, Montana, US
Material
- (UCMP 128365) proximal tarsometatarsus (UCMP online)
(UCMP 128366) distal tarsometatarsus (UCMP online)

Carinatae Merrem, 1813
Definition- (Passer domesticus <- Hesperornis regalis) (modified from Cracraft, 1986)
Other definitions- (Ichthyornis dispar + Passer domesticus) (Sereno, in press; modified from Chiappe, 1995)
(keeled sternum homologous with Vultur gryphus) (Gauthier and de Queiroz, 2001)
Diagnosis- dentary toothless (also in Archaeorhynchus and Longicrusavis); dentary symphysis fused; dorsal centra lack lateral excavations (also in Patagopteryx); no supratrochlear fossa excavating proximal surface of pisiform process (unknown in Hesperornithes); postacetabular process horizontally oriented (also in Ichthyornis);

unnamed ornithuromorph (Parris and Hope, 2002)
Late Maastrichtian-Early Danian, Late Cretaceous-Early Paleocene
Hornerstown Formation, New Jersey, US

Material- (NJSM 15065) proximal scapula
Comments- This specimen closely resembles both Ambiortus and Lithornis in the flattened, styloid, ventrally bent acromion. It may resemble the former in fusing the coracoid tubercle to the cranial end of the humeral facet. Parris and Hope (2002) tentatively referred it to Palaeognathae, but based on Clarke's (2002) placement of Ambiortus outside that clade, it is assigned to a more inclusive clade here.
References- Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT, 532 pp.
Parris and Hope, 2002. New interpretations of the birds from the Navesink and Hornerstown Formations, New Jersey, USA (Aves: Neornithes). In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing, 1-4 June 2000. 113-124.

Ambiortiformes Kurochkin, 1982
Definition- (Ambiortus dementjevi <- Passer domesticus) (Martyniuk, 2012)
= Ambiortidae Kurochkin, 1982
= Apsaraviformes Livezey and Zusi, 2007
Definition- (Apsaravis ukhaana <- Passer domesticus) (Martyniuk, 2012)
= "Apsaravidae" Livezey and Zusi, 2007
= Palintropiformes Longrich, Tokaryk and Field, 2011
Definition- (Palintropus retusus <- Hesperornis regalis, Ichthyornis dispar, Passer domesticus) (modified from Longrich et al., 2011)
Comments- Kurochkin (1982) established the monotypic Ambiortiformes and Ambiortidae, but later (1999) assigned Otogornis to the Ambiortiformes as well, and even later (2000) to the Ambiortidae. This was based on several problematic characters. The acrocoracoid of Otogornis is not noticably thicker than Enantiornis, which also shares the "three edged" morphology. The proximal tip of Otogornis' acrocoracoid is not necessarily acute (compare medial view of left coracoid to other figures). The glenoid on the scapula is no wider in Ambiortus than Enantiornis and appears concave in Hou's original illustration, but is flat in some enantiornithines (e.g. Gobipteryx) anyway. Otogornis' humeral head is no more ventrally placed than Sinornis', and is not smaller or shorter. Nor is it oval, having a proximally concave margin as in enantiornithines. Finally, the long and thin manual phalanx II-2 is symplesiomorphic, being found in most basal birds. Otogornis seems to be an enantiornithine instead. Martyniuk (2012) later defined the clade.
Livezey and Zusi (2007) named Apsaraviformes and "Apsaravidae" as monotypic and redundant taxa including only Apsaravis. "Apsaravidae" is a nomen nudum as it was only included in a table, without definition or diagnosis (ICZN Article 13.1.1). Martyniuk defined Apsaraviformes, but here it is a junior synonym of Ambiortiformes.
Longrich et al. (2011) erected Palintropiformes for Palintropus and Apsaravis, which they found formed a clade based on a version of Clarke's matrix.
Diagnosis- (proposed) capital groove absent in humerus.
References- Kurochkin, 1982. Novyy otryad ptits iz nizhnego mela Mongolii. Doklandy Akademii Nauk SSSR. 262(2), 452-455.
Kurochkin, 1999. The relationships of the Early Cretaceous Ambiortus and Otogornis (Aves: Ambiortiformes). in Olson (ed). Avian Paleontology at the Close of the 20th Century: Proceedings of the 4th International Meeting of the Society of Avian Paleontology and Evolution. Smithsonian Contributions to Paleobiology. 89, 275-284.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Livezey and Zusi, 2007. Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. Zoological Journal of the Linnean Society. 149 (1), 1-95.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K–Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Ambiortus Kurochkin, 1982
A. dementjevi Kurochkin, 1982
Hauterivian-Barremian, Early Cretaceous
Andaikhudag (= Anda Khooduk) Formation, Mongolia

Holotype- (PIN 3790-271/272) (~270 mm) axis fragment, fourteen postaxial cervical vertebrae, three anterior dorsal vertebrae, dorsal vertebral fragment, dorsal rib fragments, incomplete scapula, incomplete coracoid, partial sternum, partial furcula, proximal humerus (~67 mm), incomplete radius, incomplete ulna, ulnare, incomplete carpometacarpus, phalanx II-1, phalanx II-2, manual ungual II, body feathers, remiges
Diagnosis- (after Kurochkin, 2001) transverse ligamental fossa proximal to bicipital crest.
(proposed) mid and posterior dorsal vertebrae without hypapophyses (unknown in Apsaravis); dorsal tubercle on acromion process; supracoracoid foramen does not penetrate coracoid (also in Patagopteryx and Gansus); medial edge of metacarpal I convex.
Other diagnoses- Kurochkin (2001) included several additional characters in his diagnosis. Tha absent capital groove is shared with Apsaravis. Most basal ornithuromorphs (e.g. Patagopteryx, Apsaravis, basal Aves) share dorsoventrally compressed acromions. The acromia of Patagopteryx and Yixianornis are equally long, while that of Apsaravis is even longer. The scapular blades of most basal ornithuromorphs except Patagopteryx are equally slender. The longitudinal groove in the posterolateral scapular blade is also present in most basal ornithuromorphs (e.g. Patagopteryx, Archaeorhynchus, Apsaravis, Yixianornis). The procoracoid process is equally long and broad in Hongshanornis and songlingornithids. Several other basal ornithuromorphs have a fossa instead of a transverse ligamental groove, but that of Apsaravis, Gansus and Ichthyornis differ in being on the bicipital crest, not proximal to it. The proximal fusion of the carpometacarpus is symplesiomorphic for ornithurines (sensu Gauthier), while the dorsoventrally compressed manual phalanx II-1 is seen in ornithuromorphs except Patagopteryx.
Comments- The holotype was discovered in 1977 and described by Kurochkin (1982) as a carinate (which was equivalent to Ornithurae then as the few known fragments of taxa intermediate between Archaeopteryx and hesperornithines were not recognized as such). Cracraft (1986) was the first to include it in a phylogenetic analysis, which placed Ambiortus in an unresolved trichotomy with Ichthyornis and Aves (his Neognathae), though enantiornithines were also placed in this position because no other ornithurines (sensu Gauthier) were known and hesperornithines were placed too basally based on their flightlessness. Sanz and Buscalioni (1992) found Ambiortus to have an uncertain position compared to Ornithurae sensu Chiappe and Enantiornithes in their cladogram.
Ambiortus a palaeognath? Kurochkin referred it to Palaeognathae in 1985 based on several characters. The long pointed acromion is also found in songlingornithids and anatoids. The supposedly wide and short acrocoracohumeral ligament scar is equally long in other basal ornithuromorphs (e.g. Archaeorhynchus, Apsaravis, Yixianornis), and mediolaterally narrower as in Gansus. The longitudinal groove on the ventral acrocoracoid face is homologized to a pit in palaeognaths, but a similar depressed area is present in Archaeorhynchus and Yixianornis. In his 1995 paper, Kurochkin added a few supposed palaeognath characters. The bicipital crest was said to be absent, but is the "slightly pronounced cranial tubercle" he described in 1999. The deltopectoral crest begins just as proximally in other basal ornithuromorphs. The glenoid facet on the coracoid is displaced dorsally in Apsaravis and Ichthyornis as well. The short and wide acrocoracoid is symplesiomorphic for ornithuromorphs. The hypocleidium is also absent in Archaeorhynchus, Yanornis, Gansus and Ichthyornis. In 1999, Kurochkin added yet more supposed palaeognath characters in his description. The dorsoventrally flattened acromion is symplesiomorphic for ornithuromorphs (e.g. Patagopteryx, Apsaravis, Galliformes). A dorsal tubercle on the acromion is also present in Iaceornis and Anas. The well developed ventral tuber is also present in Archaeorhynchus, Yixianornis and Alamitornis. The "remarkable cranial tubercle" with an anterior pit is the bicipital crest, which also has such a pit in enantiornithines and Apsaravis. The strongly laterally projecting, posteriorly placed "caudal transverse processes" seem to be laterally flared postzygapophyseal processes instead, as seen in Ichthyornis.
Hope (2002) states several characters (capital groove; pneumotricipital fossa; ventral tuber; bicipital crest) are poorly developed in Ambiortus, Ichthyornis, palaeognaths and galliforms compared to most neognaths and enantiornithines. She attributes this either to convergence in the latter groups or placement of Ambiortus in Palaeognathae. Yet the first three characters are well developed in Lithornis and tinamiforms, while the bicipital crest is extremely reduced in neognaths in addition to tinamiforms. Given the distribution of characters in recently discovered basal ornithuromorphs, Ambiortus and Apsaravis lost their capital grooves independently of ratites, pneumotricipital fossae developed convergently in some enantiornithines and Aves, ventral tuber size is quite homoplasic, and a low bicipital crest is primitive for ornithuromorphs.
In conclusion, nearly all of the proposed palaeognath characters in Ambiortus are symplesiomorphic, with the exception of the dorsal acromion tubercle.
Ambiortus an ichthyornithine? Martin (1987) believed Ambiortus was the sister taxon to Apatornis (based on the Iaceornis holotype) within Ichthyornithiformes because of their long acromia, but those of Apsaravis, Yixianornis and Patagopteryx are also elongate, as are most enantiornithes'.
Chatterjee (1999) found Ambiortus to clade with Ichthyornithiformes in his analysis. This was based on the supposedly amphicoelous cervicals (actually heterocoelous in Ambiortus- Kurochkin, 1999) and absent bicipital crest (actually present in both Ambiortus and Ichthyornis).
Ambiortus a basal ornithuromorph? Sereno and Rao (1992) found Ambiortus to be an ornithuromorph outside of Ornithurae sensu Chiappe based on an unpublished phylogenetic analysis, but this cannot be evaluated.
Elzanowski (1995) placed Ambiortus in basal Ornithuromorpha (his Neornithes), excluded from Aves (his Neognathae) due to the dorsally projecting deltopectoral crest and lack of an extensor process on metacarpal I, and excluded from Carinatae (unnamed node in his cladogram, not equivalent to his Carinatae) based on the more laterally facing scapular glenoid and prominent acromion process. The deltopectoral crest is anteriorly projecting in patagopterygids, but otherwise seems to be an unambiguous avian character. As described and illustrated by Kurochkin (1999), Ambiortus actually has an extensor process, albeit a low one. Small acromia are also present in Archaeorhynchus and Hongshanornis but absent in the very derived Iaceornis, so show some homoplasy. The glenoid does seem less dorsally angled than carinates.
Chiappe (2001) placed Ambiortus closer to Aves than Patagopteryx based on the procoracoid process (also absent in Apsaravis) and proximally globe-shaped humeral head. It was excluded from Carinatae due to the absent extensor process (again miscoded, as it is actually present but low) and the presence of manual ungual II (miscoded as absent in Ichthyornis based on an Iaceornis element, but still valid to exclude Ambiortus from an Iaceornis+Aves clade). While placed between Hesperornithes and Ichthyornis on his cladogram, Chiappe later (2002) noted it could equally parsimoniously be placed as sister to Ornithurae (sensu Chiappe).
Clarke (2002) first included Ambiortus in her unpublished thesis' matrix, finding it positioned above Patagopteryx, but in a polytomy with Apsaravis, Gansus, Hesperornithes, Ichthyornis, Limenavis and Iaceornis+Aves. It was first published in a version of Clarke's matrix by You et al. (2006), which presents Ambiortus as falling out more derived that Patagopteryx and Hongshanornis, but more basal than Apsaravis, songlingornithids, Gansus and ornithurines (sensu Chiappe). The supplementary information indicates it also emerged as a songlingornithid in some trees. In the first position, Ambiortus was more derived than Patagopteryx and Hongshanornis based on the absent hypocleideum, proximally domed humeral head, extensor process on metacarpal I, and highly compressed manual phalanx II-1. It was less derived than Aves based on several characters- acrocoracoid process not hooked medially; pit on bicipital crest absent (miscoded in Ambiortus); extensor process on metacarpal I not projecting; thick metacarpal III (which cannot actually be coded, as only the fused base is preserved); phalanx II-2 longer than II-1 (miscoded in Ambiortus).
While several characters were miscoded by various authors, Ambiortus does seem excluded from Aves based on- scapular glenoid less dorsally angled; acrocoracoid not medially hooked; dorsally projecting deltopectoral crest; low extensor process on metacarpal I; manual ungual II absent.
References- Kurochkin, 1982. Novyy otryad ptits iz nizhnego mela Mongolii. Doklandy Akademii Nauk SSSR. 262(2), 452-455.
Kurochkin, 1983. New order of birds from the Lower Cretaceous in Mongolia. Palaeontological Journal. 17, 215-218.
Kurochkin, 1985. Lower Cretaceous birds from Mongolia and their evolutionary significance. XVIII Congressus Internationalis Ornithologicus: Programme. 1, 191-199.
Kurochkin, 1985. A true carinate bird from Lower Cretaceous deposits in Mongolia and other evidence of Early Cretaceous birds in Asia. Cretaceous Research. 6, 271-278.
Cracraft, 1986. The origin and early diversification of birds. Paleobiology. 12, 383-399.
Martin, 1987. The beginning of the modern avian radiation. Documents des Laboratoires de Geologie de la Faculte des Sciences de Lyon. 99, 9-20.
Sanz and Buscalioni, 1992. A new bird from the Early Cretaceous of Las Hoas, Spain, and the early radiation of birds. Palaeontology. 35, 829-845.
Sereno and Rao, 1992. Early evolution of avian flight and perching: New evidence from Lower Cretaceous of China. Science. 255, 845-848.
Elzanowski, 1995. Cretaceous birds and avian phylogeny. Courier Forschungsinstitut Senckenberg. 181, 37-53.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Kurochkin, 1996. Morphological differentiation of palaeognathous and neognathous birds. Courier Forschungsinstitut Senckenberg. 181, 79-88.
Kurochkin, 1999. The relationships of the Early Cretaceous Ambiortus and Otogornis (Aves: Ambiortiformes). in Olson (ed). Avian Paleontology at the Close of the 20th Century: Proceedings of the 4th International Meeting of the Society of Avian Paleontology and Evolution. Smithsonian Contributions to Paleobiology. 89, 275-284.
Chiappe, 2001. Phylogenetic relationships among basal birds. In Gauthier and Gall (eds). New perspectives on the origin and early evolution of birds: Proceedings of the international symposium in honor of John H. Ostrom. New Haven: Peabody Museum of Natural History. 125-139.
Kurochkin, 2001. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.

Apsaravis Norell and Clarke, 2001
A. ukhaana Norell and Clarke, 2001
Late Campanian, Late Cretaceous
Djadokhta Formation, Mongolia
Holotype
- (IGM 100/1017) partial jugal, posterior skull, sclerotic ring, incomplete mandible, twelve cervical vertebrae, six dorsal vertebrae (4.5 mm), fragmentary dorsal ribs, synsacrum (28.6 mm), five caudal vertebrae (2.04 mm), partial pygostyle, scapulae (~52.5 mm), coracoids (29.25 mm), anterior sternum, humeri (48.43 mm), radii (43.11 mm), ulnae (45.69 mm), radiale, ulnare, incomplete carpometacarpi, phalanx II-1 (~9.62 mm), ilia (31.5 mm), pubes (one proximal; 30.14 mm), ischia (30.14 mm), proximal femora (~40.9 mm), distal tibiotarsi, tarsometatarsi (28.7 mm), phalanges II-1, phalanges II-2, pedal ungual II, phalanges III-1 (one proximal), phalanx III-2, phalanx III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanx IV-3, pedal ungual IV, several pedal phalanges, ossified tarsometatarsal tendon
Diagnosis- (after Norell and Clarke, 2001) dentary forked posteriorly (unknown in Ambiortus; also in Yixianornis+Songlingornis); strong tubercle on the proximal posterior surface of the humerus directly distal to the humeral head; distal humerus strongly flared and anteroposteriorly compressed (unknown in Ambiortus); humeral distal condyles strap-like (unknown in Ambiortus); dorsal condyle of humerus transversely oriented (unknown in Ambiortus); ventral condyle of humerus strongly projected distally (unknown in Ambiortus); enlarged lateral ridge on the femur (unknown in Ambiortus; also in hesperornithines); medial tibiotarsal condyle <60% the width of the lateral condyle (unknown in Ambiortus; also in Longicrusavis); tibiotarsal condyles do not slope towards center in distal view (unknown in Ambiortus; also in Longicrusavis); tibiotarsal intercondylar groove less than 30% as wide as distal condyles (unknown in Ambiortus); well-projected wings of the sulcus cartilaginis tibialis on the posterodistal tibiotarsus.
(after Clarke and Norell, 2002) laterally hooked acromion process (also in Yanornis); metatarsal II non-ginglymoid (unknown in Ambiortus; also in some hesperornithines and Yanornis).
(proposed) procoracoid process absent; deep dorsal fossa on coracoid; medial area of coracoid depressed where supracoracoid foramen is (unknown in Ambiortus; also in derived hesperornithines); proximoposterior surface of deltopectoral crest concave (also in Ichthyornis); brachial fossa on humerus poorly developed (also in derived hesperornithines); no indication of muscle origins on dorsodistal edge of humerus (unknown in Ambiortus; also in Yixianornis); well developed bicipital tubercle on ulna (unknown in Ambiortus; also in Yixianornis and Ichthyornis); posterior trochanter on femur (unknown in Ambiortus); extensor canal absent in tibiotarsus (unknown in Ambiortus); only one proximal vascular foramen in tarsometatarsus (unknown in Ambiortus).
Other diagnoses- Norell and Clarke (2001) also use the scapular blade which does not expand at midlength in their diagnosis, though Clarke and Norell (2002) later exclude it from their diagnosis and analysis, citing difficulty in defining it objectively. In any case, such a scapula is also present in songlingornithids and Hesperornis, making its presence in Patagopteryx, Ichthyornis and Ambiortus equally likely to be convergent as it is to be developed basally in Ornithuromorpha and lost by Apsaravis. Norell and Clarke note a supposedly apomorphic hypertrophied trochanteric crest on the femur, which is also described and photographed by Clarke and Norell. However, this structure is a posterolaterally projected crest distal to the femoral head, which is unlike trochanteric crests but like the lateral ridge of more basal maniraptorans which is derived from the trochanteric shelf. Whether the lateral ridge's size is apomorphic is uncertain, as hesperornithines have an even larger bulge and Patagopteryx and Gansus have small tubercles. Another less developed vertical ridge is present posterior to this, which could also be homologized to the trochanteric shelf. However, topologically, this would be equivalent to the posterior trochanter.
Clarke and Norell (2002) also add a fused dentary symphysis to their diagnosis, but that is optimized as a carinate character here.
Comments- The holotype was discovered in 1998 and described briefly in 2001 by Norell and Clarke, then in detail the next year (Clarke and Norell, 2002). It was originally placed as the sister taxon to Carinatae, but Clarke (2002) and Clarke and Norell (2002) found it to be the sister group of Ornithurae sensu Chiappe instead. This result has been found in further permutations of Clarke's matrix as well (e.g. You et al., 2006; O'Connor et al., 2009).
References- Clarke and Norell, 2001. Fossils and avian evolution. Nature. 414, 508.
Feduccia, 2001. Fossils and avian evolution. Nature. 414, 507-508.
Norell and Clarke, 2001. Fossil that fills a critical gap in avian evolution. Nature. 409, 181-184.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke and Norell, 2002. The morphology and phylogenetic position of Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum Novitates. 3387, 1-46.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
O'Conner, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.

Palintropus Brodkorb, 1970
Diagnosis- (after Longrich, 2009) acrocoracoid process massive and knob-like (also in Gansus and Ichthyornis); edge of humeral articular facet with a prominent lip in ventral view (also in Yixianornis); prominent scar inside supracoracoid sulcus (unknown in most non-avian euornithines).
Other diagnoses- Marsh (1892) first noted the absent procoracoid process as diagnostic, but this is shared with Apsaravis.
Here I interpret the very large, centrally and distally placed supracoracoid foramen noted as diagnostic by Hope (2002) as the proximal edge of a dorsal coracoid fossa as in Apsaravis. This same feature was described as "prominent dorsal groove in coracoid shaft" by Longrich (2009).
Longrich also included the supracoracoid foramen opening into a medial groove of the coracoid shaft, which is shared with Apsaravis.
Comments- Marsh (1892) originally included retusus in Cimolopteryx, as C. retusa. Shufeldt (1915) noted it was not referrable to Cimolopteryx and probably not even closely related, though he felt it was too fragmentary for further evaluation. Brodkorb (1963) first removed it to Apatornis, which he viewed as an ichthyornithine. He then (1970) placed it in a new genus Palintropus, which he believed was a cimolopterygid charadriiform.
Palintropus a galliform? Hope (2002) questionably referred this taxon to Galliformes. This was based on the reduced procoracoid process, coracoid facet for scapula placed entirely distal to glenoid. Several other characters were listed in Hope's Galliformes diagnosis as being reasons why she placed "specimens below" (consisting solely of Palintropus) in that order, but are eithjer undescribed (coracoid neck with stout and triangular cross section) or unknown (elongate coracoid shaft; narrow sternal end of coracoid; rudimentary lateral process) in that genus. She also noted the acrocoracoid was similar in size to galliforms (larger than tinamiforms, smaller than anseriforms and most neoavians), the absence of a pneumatic foramen is unlike tinamiforms, and the laterally positioned coracoid tubercle which merges with the glenoid is similar to galliforms. However, the procoracoid process is also absent in Patagopteryx and (as noted by Longrich, 2009) Apsaravis, while it is still present though reduced in basal galliforms like Paraortygoides, Paraortyx and Ameripodius. I also note Apsaravis has a coracoid facet placed distal to the glenoid. Lack of coracoid pneumatization is present in all non-avians (except perhaps Jixiangornis and Jianchangornis). The laterally positioned coracoid tubercle that merges with the glenoid is also found in galliforms, tinamiforms, Lithornis, Patagopteryx, Yixianornis, Jianchangornis, Ichthyornis and Ambiortus, so seems symplesiomorphic for Aves. Gansus and Ichthyornis also have moderate sized acrocoracoid processes.
Hope referred it questionably to the basal galliform family Quercymegapodiidae based on the large free lateral flange on the coracoid glenoid, further reduced procoracoid process (only with Quercymegapodius and not Ameripodius), and scar within the supracoracoid sulcus (only verified in Ameripodius). Also she correctly noticed the deep cup-like scapular facet is unlike crown galliforms. Apsaravis, Ichthyornis, Gansus, Yixianornis, Patagopteryx and Archaeorhynchus also have a large lateral flange on the coracoid glenoid. Almost all non-avian euornithines also have scapular cotyla which are deeper than those of crown galliforms. The texture of the supracoracoid sulcus is generally indeterminable in non-avian euornithines, even when they expose the sulcus as in Yixianornis. Hope, Mayr (2009) and Longrich all noted that it was unlike Tertiary Galliformes in having a supracoracoid foramen, and Longrich stated it differed further in lacking a strongly hooked acrocoracoid.
Thus Palintropus does not share any characters with galliforms not seen in Apsaravis except for the larger acrocoracoid (which is also seen in some non-avian euornithines). As Palintropus has some characters which exclude it from Galliformes, and the only character shared with a quercymegapodiid (the supracoracoid sulcus scar) is indeterminate in Apsaravis and most other non-avian euornithines, it is near certainly not a member of Quercymegapodiidae.
Palintropus related to Apsaravis? Longrich (2009) suggested Palintropus was related to Apsaravis based on the absent procoracoid process and medial supracoracoid groove. They also seem to share a deep dorsal fossa in the coracoid. While these characters are also shared with most enantiornithines, the scapulocoracoid articulation is unlike that clade. The referred dorsal and femur also lack enantiornithine synapomorphies (e.g. they have anteriorly placed parapophyses and no posterior trochanter). Longrich et al. (2011) included Palintropus in a version of Clarke's matrix where it claded with Apsaravis, but did not include basal galliforms that could test Hope's hypothesis. When added to a modified version of Clarke's phylogenetic analysis of birds (with basal galliforms such as Paraortygoides, Quercymegapodius and Ameripodius also added), Palintropus emerges as sister to Apsaravis. Longrich's hypothesis is thus supported.
References- Marsh, 1892. Notes on Mesozoic vertebrate fossils. American Journal of Science. 55, 171-175.
Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Brodkorb, 1970. The generic position of a Cretaceous bird. Quarterly Journal of the Florida Academy of Science. 32(3), 239-240.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Mayr, 2009. Paleogene Fossil Birds. Springer-Verlag, Heidelberg & New York. 262 pp.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K–Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.
P. retusus (Marsh, 1892) Brodkorb, 1970
= Cimolopteryx retusa Marsh, 1892
= Apatornis retusus (Marsh, 1892) Brodkorb, 1963
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Holotype
- (YPM 513) proximal coracoid
Diagnosis- (after Longrich, 2009) smaller than both Campanian species; lacks kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process shorter and more expanded; humeral articular facet broader anteriorly than posteriorly; dorsal groove extends to level of scapular cotyle.
Comments- The holotype was discovered in 1980.
References- Marsh, 1892. Notes on Mesozoic vertebrate fossils. American Journal of Science. 55, 171-175.
Brodkorb, 1963. Birds from the Upper Cretaceous of Wyoming. in Sibley (ed.). Proceedings of the XIII International Ornithological Congress. 50-70.
Brodkorb, 1970. The generic position of a Cretaceous bird. Quarterly Journal of the Florida Academy of Science. 32(3), 239-240.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
P. sp. nov. (Hope, 2002)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material-
(RTMP 86.36.126) proximal coracoid (Hope, 2002)
?(RTMP 89.81.12) dorsal vertebra (Longrich, 2009)
?(RTMP 2001.12.150) distal femur (Longrich, 2009)
Diagnosis- (after Longrich, 2009) over twice as large as P. retusus, a third larger than the other Campanian species; kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process shorter and more expanded; humeral articular facet broader anteriorly than posteriorly; dorsal groove extends to level of scapular cotyle.
Comments- Hope (2002) referred RTMP 86.36.126 to a new species of Palintropus, along with RTMP 86.146.11, 88.116.1 and five other RTMP specimens. She noted some of these specimens were smaller, so might belong to another species, or that Palintropus may have been sexually dimorphic. Longrich referred RTMP 86.36.126 to his Palintropus species A, along with a dorsal vertebra and femur based on their size.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
P. sp. nov. (Longrich, 2009)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada

Material- (RTMP 83.36.70) coracoid fragment (Longrich, 2009)
(RTMP 88.116.1) proximal coracoid (Hope, 2002)
?(RTMP 89.50.53) dorsal vertebra, partial synsacrum (Longrich, 2009)
(RTMP 92.53.3) coracoid fragment (Longrich, 2009)
?(RTMP 96.12.336) femur (Longrich, 2009)
(RTMP 2005.12.190) partial coracoid (Longrich, 2009)
Late Campanian, Late Cretaceous
Foremost Formation, Alberta, Canada

?(RTMP 86.146.11) proximal scapula (Hope, 2002)
Diagnosis- (after Longrich, 2009) intermediate in size between other species; lacks kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process taller and less expanded; humeral articular facet strongly semicircular; dorsal groove does not extend to level of scapular cotyle.
Comments- Hope (2002) referred RTMP 86.146.11 and 88.116.1 to the same undetermined Palintropus species as RTMP 86.36.126, though she noted the latter might belong to a different species or sex. Longrich (2009) placed the former specimens in his new Palintropus species B, which he stated differed markedly in morphology from P. retusus or P. species A.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
P. sp. (Hope, 2002)
Late Campanian, Late Cretaceous
Belly River Group, Alberta, Canada

Material- (RTMP coll.) three partial coracoids (Hope, 2002)
Comments- Hope (2002) referred five coracoids in the RTMP collections to her new Palintropus species, two of which are probably RTMP 83.36.70 and 92.53.3 that were later mentioned by Longrich (2009) and referred to his Palintropus species B. Whether the other three belong to P. species A or B is unknown.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.