Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and Potamornis, all strong-swimming, predatory divers. Many of the species most specialized for swimming were completely flightless. The largest known hesperornithean, Canadaga arctica, may have reached a maximum adult length of over 1.5 metres (4.9 ft).

Hesperornitheans were the only Mesozoic avialans to colonize the oceans. They were wiped out in the Cretaceous–Paleogene extinction event, along with enantiornitheans and all other non-avian dinosaurs, as well as many other diverse plant and animal groups.

Temporal range:
Late Cretaceous, 100–66 Ma
Hesperornis regalis (1)
Restored skeleton of Hesperornis regalis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Ornithurae
Clade: Hesperornithes
Fürbringer, 1888

Hesperornithiformes Sharpe, 1899[3]

Anatomy and ecology

Hesperornis BW
Life restoration of Hesperornis regalis

Most of what is known about this group rests on analyses of single species, as few provide sufficiently complete fossils for analysis. Although some of the smaller and more primitive species, like those belonging to the subgroups Enaliornithidae and Brodavidae, might have been able to fly, the larger hesperornithids like Hesperornis and Baptornis had only vestigial wings. As in the case of modern foot-propelled diving birds, the femur and metatarsus of these animals were short, whereas the tibia was long. The legs were also set far back on the body, as in loons, grebes or penguins. Hesperornithids must have been powerful swimmers and divers but extremely ungainly on the land, and probably spent little time ashore except to nest. They were rather long-bodied, and measured about 6 feet (180 cm) long.[5]

Some researchers think that on land they had to slide on their bellies and push with their legs; the hip and knee joints were shaped such that these species could not move them dorsoventrally, and in a resting position the feet projected sideways from the body, which would have prevented them from walking upright.[1] The anatomy of their toes suggests that hesperornitheans had lobes of skin for propulsion underwater similar to grebes, rather than being webbed. The dense bones of these animals decreased their buoyancy, making diving easier.[6] Homever, morphometric comparison with modern diving birds suggests that herperornitheans share more similarities with diving ducks and cormorants rather than with loons or grebes.[7]

The snout was long, and tipped with a slightly hooked beak. Behind the beak, the jaws were filled with a series of simple, sharp teeth which were set into a longitudinal groove. These probably helped to seize fish, like the serrated beak of mergansers; unlike the reptilian teeth of more primitive avialans, those of the hesperornithids were unique.[8][9] They also retained a dinosaur-like joint between the lower jaw bones. It is believed that this allowed them to rotate the back portion of the mandible independently of the front, thus allowing the lower teeth to disengage.[5]


Currently, the hesperornitheans are recognized as a very specialized lineage that is not ancestral or otherwise closely related to birds. Still, their relationship is close enough that they probably diverged from the ancestors of modern birds as late as the earliest Cretaceous.

The earliest known hesperornithine is the Early Cretaceous Enaliornis. The majority of hesperornithean species are known from the Late Cretaceous of North America. Small hesperornithean bones are known from the freshwater deposits of the Late Cretaceous of the Judith River Group as well as the Hell Creek and Lance Formations, and in several Eurasian sites. These species were about the size of a cormorant or a loon.


The clade Hesperornithes was originally named as a subclass of Aves by Furbringer in 1888.[10] However, it was generally ignored in the scientific literature in favor of the order-level name Hesperornithiformes, coined one year later. In 2004, Clarke became the first to define the hesperornithean group in terms of phylogenetics. Clarke defined Hesperornithes as all species closer to Hesperornis regalis than to modern birds, and regarded Hesperornithiformes as a junior synonym, though she did not define the latter name. Clarke also defined the more inclusive group Hesperornithidae as all hesperornitheans closer to Hesperornis than to Baptornis.[3]

Hesperornitheans were originally combined with Ichthyornis in the paraphyletic group "Odontornithes" by Othniel Charles Marsh, in 1873. In 1875, they were separated as Odontolcae. The group was often considered to be related to loons and grebes,[11] or to the Paleognathae (based on perceived similarities in the bony palate).[12] These similarities, however, as the more recently determined fact that the osteons of their bones – at least in Hesperornis – were arranged in a pattern similar to that in Neognathae,[13] are today considered to be due to convergent evolution.[14][15]


In 2015, a species-level phylogenetic analysis found the following relationships among hesperornithiforms.[16]





AMNH 5101

FMNH 395

Baptornis advenus


Brodavis varneri

Brodavis baileyi

Fumicollis hoffmani


Parahesperornis alexi



Hesperornithiformes Fürbringer 1888 [Dromaeopappi Stejneger 1885; Odontornithes Forbes 1884; Odontolcae Stejneger 1875; Hesperornithomorphi Hay 1930; Odontognathe Wetmore 1930] {Odontoholcae Stejneger 1885: Hesperornithes Fürbringer 1888}[17][18]


  1. ^ a b Larry D. Martin; Evgeny N. Kurochkin; Tim T. Tokaryk (2012). "A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia". Palaeoworld. 21: 59–63. doi:10.1016/j.palwor.2012.02.005.
  2. ^ Tomonori Tanaka; Yoshitsugu Kobayashi; Ken'ichi Kurihara; Anthony R. Fiorillo; Manabu Kano (2017). "The oldest Asian hesperornithiform from the Upper Cretaceous of Japan, and the phylogenetic reassessment of Hesperornithiformes". Journal of Systematic Palaeontology. Online edition. doi:10.1080/14772019.2017.1341960.
  3. ^ a b c Clarke, J. A. (2004). "Morphology, Phylogenetic Taxonomy, and Systematics of Ichthyornis and Apatornis (Avialae: Ornithurae)" (PDF). Bulletin of the American Museum of Natural History. 286: 1–179. doi:10.1206/0003-0090(2004)286<0001:MPTASO>2.0.CO;2. hdl:2246/454.
  4. ^ Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
  5. ^ a b Perrins, Christopher (1987) [1979]. "Bird Families of the World". In Harrison, C.J.O. (ed.). Birds: Their Lifes, Their Ways, Their World. Reader's Digest Association, Inc. pp. 165–167. ISBN 978-0895770653.
  6. ^ Chinsamy, A.; Martin, Larry D.; Dobson, P. (1998). "Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas". Cretaceous Research. 19 (2): 225. doi:10.1006/cres.1997.0102.
  7. ^ Bell, Alyssa; Wu, Yun-Hsin; Chiappe, Luis M. (2019). "Morphometric comparison of the Hesperornithiformes and modern diving birds". Palaeogeography, Palaeoclimatology, Palaeoecology. 513: 196–207. Bibcode:2019PPP...513..196B. doi:10.1016/j.palaeo.2017.12.010.
  8. ^ Marsh, Othniel Charles (1880): Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
  9. ^ Gregory, Joseph T. (1952). "The Jaws of the Cretaceous Toothed Birds, Ichthyornis and Hesperornis" (PDF). Condor. 54 (2): 73–88. doi:10.2307/1364594. JSTOR 1364594.
  10. ^ Fürbringer, M. (1888): Untersuchungen zur Morphologie und Systematik der Vögel (2 vols). Von Holkema, Amsterdam.
  11. ^ Cracraft, Joel (1982). "Phylogenetic relationships and monophyly of loons, grebes, and hesperornithiform birds, with comments on the early history of birds". Systematic Zoology. 31 (1): 35–56. doi:10.2307/2413412. JSTOR 2413412.
  12. ^ Gingerich, P. D. (1973). "Skull of Hesperornis and the early evolution of birds". Nature. 243 (5402): 70–73. Bibcode:1973Natur.243...70G. doi:10.1038/243070a0.
  13. ^ Houde, Peter (1987). "Histological evidence for the systematic position of Hesperornis (Odontornithes: Hesperornithiformes". The Auk. 1045 (1): 125–129. doi:10.2307/4087243. JSTOR 4087243.
  14. ^ Stolpe, M. (1935). "Colymbus, Hesperornis, Podiceps: ein Vergleich ihrer hinteren Extremität". Journal für Ornithologie (in German). 83: 115–128. doi:10.1007/BF01908745.
  15. ^ Bogdanovich, I.O. (2003). "Морфологiчнi аспекти філогеніі Hesperornithidae (Ornithurae, Aves)" [Morphological Aspects of the Phylogeny of the Hesperornithidae (Ornithurae, Aves)] (PDF). Vestnik Zoologii (in Ukrainian, Russian, and English). 37 (6): 65–71.
  16. ^ Bell, A.; Chiappe, L. M. (2015). "A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds". Journal of Systematic Palaeontology. 14 (3): 239–251. doi:10.1080/14772019.2015.1036141.
  17. ^ Mikko's Phylogeny Archive [1] Haaramo, Mikko (2007). "†Hesperornithiformes". Retrieved 30 December 2015.
  18. ^ Paleofile.com (net, info) "Archived copy". Archived from the original on 2016-01-11. Retrieved 2015-12-30.CS1 maint: archived copy as title (link). "Taxonomic lists- Aves". Archived from the original on 11 January 2016. Retrieved 30 December 2015.

Asiahesperornis is a prehistoric foot-propelled diving toothed flightless bird genus from the Late Cretaceous. The single known species is Asiahesperornis bazhanovi. It lived in what today is Kazakhstan, at its time the shores of the shallow Turgai Sea.It was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous. Its exact relationships are not completely resolved, but it probably belongs into the Hesperornithidae just like Hesperornis, well-known from the Western Interior Seaway that covered most of the US Midwest in the Mesozoic. Its name is derived from its findings in Asia.


Avebrevicauda (meaning "birds with short tails") is a group which includes all avialan species with ten or fewer free vertebrae in the tail. The group was named in 2002 by Gregory S. Paul to distinguish short-tailed avialans from their ancestors, such as Archaeopteryx, which had long, reptilian tails.The cladogram below follows the results of a phylogenetic study by Wang et al., 2016.


Baptornis ("diving bird") is a genus of flightless aquatic birds from the Late Cretaceous, some 87-80 million years ago (roughly mid-Coniacian to mid-Campanian faunal stages). The fossils of Baptornis advenus, the type species, were discovered in Kansas, which at its time was mostly covered by the Western Interior Seaway, a shallow shelf sea. It is now known to have also occurred in today's Sweden, where the Turgai Strait joined the ancient North Sea; possibly, it occurred in the entire Holarctic.

Othniel Charles Marsh discovered the first fossils of this bird in the 1870s. This was, alongside the Archaeopteryx, one of the first Mesozoic birds to become known to science.


Brodavis is a genus of freshwater hesperornithiform birds known from the Late Cretaceous (possibly Campanian and Maastrichtian stage) of North America and Asia. It was first described and named by Larry D. Martin, Evgeny N. Kurochkin and Tim T. Tokaryk in 2012 and assigned to a new monogeneric family, Brodavidae. Four species were described and assigned to Brodavis.

The type species, B. americanus, is known from the holotype left metatarsal, RSM P 2315.1 which was collected in the Maastrichtian-age Frenchman Formation of Canada.

B. baileyi is known from the holotype left metatarsal, UNSM 50665, which was collected in the Maastrichtian-age Hell Creek Formation of South Dakota, United States (dated to between 66.8 and 66 Ma ago)

B. mongoliensis is known from the holotype left metatarsal, PIN 4491-8, which was collected in the Maastrichtian-age Nemegt Formation of Mongolia.

B. varneri was originally named as a second species of Baptornis by James Martin and Amanda Cordes-Person in 2007. It is based on the holotype left tarsometatarsal SDSM 68430 which was collected in the Campanian-age Sharon Springs Formation, lower Pierre Shale of southwestern South Dakota (dated to between 81.5 and 80.5 million years ago.). "Baptornis" varneri might represent a fourth species of Brodavis or belong to a separate genus.

Brodavis is considered to be the first freshwater and latest record of the order Hesperornithiformes. Although hesperornithiforms probably lost their flight abilities by the end of the Early Cretaceous, minimal pachyostosis in Brodavis suggests the possibility of some volant abilities.


Canadaga (meaning "Canadian bird") is a flightless bird genus from the Late Cretaceous. The single known species is Canadaga arctica. It lived in the shallow seas around what today is Bylot Island in Nunavut, Canada. Its fossils were found in rocks dated to the mid-Maastrichtian age, about 67 million years ago.It was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous. Among these, it belonged to the Hesperornithidae, along with Hesperornis, the well-known namesake genus.C. arctica is one of the largest known members of the Hesperornithes, reaching a length of 1.5 metres (4.9 ft). It also represents one of the last known members of the lineage. Unlike its relatives which are mainly known from subtropical or tropical waters, this species seems to have ranged in temperate or even subarctic areas.


Enaliornis is a genus of hesperornithine birds which lived in the early Late Cretaceous, making them the oldest known hesperornithines. Fossils have been found near Cambridge, England. Due to its lack of certain hesperornithid apomorphies, they were much more "conventional" birds and were initially held to be Gaviiformes (loons/divers).


Euornithes (from Greek ευόρνιθες euórnithes meaning "true birds") is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to Sinornis.


Fumicollis is a genus of prehistoric flightless birds from the Late Cretaceous (Coniacian-Santonian) Niobrara Chalk of Kansas.


Gallornis is a genus of prehistoric birds from the Cretaceous. The single known species Gallornis straeleni lived near today's Auxerre in Yonne département (France); it has been dated very tentatively to the Berriasian-Hauterivian stages, that is about 140–130 million years ago. The known fossil material consists of a worn partial femur and a fragment of the humerus.This is a highly significant taxon for theories about the evolution of birds. Unfortunately, it is not known from much or well-preserved material. It has been proposed that the remains show features only known from the Neornithes – the group of birds that exists today. Thus, the Gallornis fossils suggest that as early as about 130 million years ago or more the ancestors of all living birds might already have been an evolutionary lineage distinct from the closely related Hesperornithes and Ichthyornithes (essentially modern birds retaining some more ancient features like teeth) and the more distantly related Enantiornithes (a group of more primitive toothed birds which were the most successful avians in the Mesozoic).


Gansus is a genus of aquatic birds that lived during the Aptian age of the Early Cretaceous (Aptian-Albian) period in what are now Gansu and Liaoning provinces, western China. The rock layers from which their fossils have been recovered are dated to 120 million years ago. It was first described in 1984 on the basis of an isolated left leg. It is the oldest-known member of the Ornithurae, the group which includes modern birds (Neornithes) and extinct related groups, such as Ichthyornis and Hesperornithes.


Gobipterygidae is a family of extinct enantiornithine birds known from the Cretaceous of Asia.


Ichthyornithes is an extinct group of toothed avialans very closely related to the common ancestor of all modern birds. They are known from fossil remains found throughout the late Cretaceous period of North America, though only one species, Ichthyornis dispar, is represented by complete enough fossils to have been named. Ichthyornitheans became extinct at the Cretaceous–Paleogene boundary, along with enantiornitheans, all other non-avian dinosaurs, and many other animal and plant groups.


Judinornis is a genus of prehistoric flightless birds from the late Cretaceous period. The single known species is Judinornis nogontsavensis. Its fossils have been found in Nemegt Formation rocks of southern Mongolia, and though the age of these deposits is not fully resolved, Judinornis probably lived some 70 million years ago during the early Maastrichtian.

The Nemegt Formation does not seem to contain marine sediments. Consequently, and unlike its relatives, this was apparently a bird of estuaries and rivers running from the mountains thrown up by the Cimmerian orogeny through the arid lands of continental East Asia towards the Turgai Sea and the former Shigatze Ocean.Judinornis was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous. Though its relationships to other members of this group are inadequately known, it appears to have been one of the more basal hesperornithines.


Ornithurae (meaning "bird tails" in Greek) is a natural group which includes the common ancestor of Ichthyornis, Hesperornis, and all modern birds as well as all other descendants of that common ancestor.


Parahesperornis is a genus of prehistoric flightless birds from the Late Cretaceous. Its range in space and time may have been extensive, but its remains are rather few and far between, at least compared with its contemporary relatives in Hesperornis. Remains are known from central North America, namely the former shallows of the Western Interior Seaway in Kansas. Found only in the upper Niobrara Chalk, these are from around the Coniacian-Santonian boundary, 85-82 million years ago (mya).

Parahesperornis alexi (Martin, 1984) was long lumped with specimen YPM 1478, described initially as Hesperornis gracilis and later moved to the monotypic genus Hargeria (Lucas, 1903). It then turned out that this genus' description actually referred to specimen KUVP 2287, which eventually became the holotype of P. alexi. Nonetheless, the taxon description of Hargeria was about "Hesperornis" gracilis exclusively, and thus despite the misidentification it applies to YPM 1478, the holotype of "H." gracilis. This mistake was rectified by later authors, who sank Hargeria back into Hesperornis.In 2017, Asiahesperornis was considered as a possible synonym of Parahesperornis.

Parahesperornis was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous and more specifically in the main lineage, close to Hesperornis. Possibly the genus extended into the Campanian, to less than 80 mya. In any case, there are two very similar fossils from the Nemegt Formation (Maastrichtian or possibly late Campanian, around 76-66 mya), which were found at Tsagaan Kushu (Mongolia). Both are distal ends of tibiotarsi, and they seem certainly more similar to the bones of Hesperornithiformes and (due to the smallish size) to Parahesperornis specifically. However, they are not very diagnostic regardless, and the diversity of Parahesperornis remains enigmatic.


Pasquiaornis is a prehistoric flightless bird genus from the Late Cretaceous. It lived during the late Cenomanian, between 95-93 million years ago.Two species have been described, P. hardiei and P. tankei. The genus Pasquiaornis was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous. Though its relationships to other members of this group are inadequately known, Pasquiaornis appears to have been one of the more basal lineages.


Patagopterygiformes is a group of extinct large Cretaceous terrestrial birds from South America. It contains at most three genera: Patagopteryx, Alamitornis and Kuszholia.


Potamornis is a prehistoric bird genus that dated back to the late Maastrichtian age of the late Cretaceous period. Its scrappy remains were found in the Lance Formation at Buck Creek, USA, and additional possible remains were found in the upper Hell Creek Formation of Montana, dated to the Danian age of the Paleogene period, though these may have been reworked. A single species was named and described in 2001: Potamornis skutchi.This was almost certainly a member of the Hesperornithes, the hefty and toothed flightless diving birds of the Mesozoic seas. Its precise relationships are not all too clear; the quadrate bone is unique in some respects but apparently shares more apomorphies with the family Hesperornithidae - the "typical" Hesperornithes - in cladistic analysis. Consequently, it might be considered a fossil hesperornithid with a different feeding specialization. Though it was heavily built like many (flying and flightless) diving birds, it weighed perhaps 1.5 or 2 kg. This raises the possibility that the Hesperornithes not only included flying members (see also Enaliornis), but that their families might have evolved flightlessness independently.


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