Hesperornis

Hesperornis (meaning "western bird") is a genus of penguin-like bird that spanned the first half of the Campanian age of the Late Cretaceous period (83.5–78 mya). One of the lesser-known discoveries of the paleontologist O. C. Marsh in the late 19th century Bone Wars, it was an early find in the history of avian paleontology. Locations for Hesperornis fossils include the Late Cretaceous marine limestones from Kansas and the marine shales from Canada. Nine species are recognised, eight of which have been recovered from rocks in North America and one from Russia.

Hesperornis
Temporal range: Late Cretaceous, 83.5–78 Ma
Hesperornis regalis (1)
Restored skeleton of H. regalis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Hesperornithes
Family: Hesperornithidae
Genus: Hesperornis
Marsh, 1872
Type species
Hesperornis regalis
Marsh, 1872
Species

H. regalis Marsh, 1872
H. crassipes (Marsh, 1876)
H. gracilis Marsh, 1876
H. altus (Marsh, 1893)
H. montana Schufeldt, 1915
H. rossicus Nesov & Yarkov, 1993
H. bairdi Martin & Lim, 2002
H. chowi Martin & Lim, 2002
H. macdonaldi Martin & Lim, 2002
H. mengeli Martin & Lim, 2002
H. lumgairi Aotsuka & Sato, 2016 (in press) [1]

Synonyms

Lestornis Marsh, 1876
Coniornis Marsh, 1893
Hargeria Lucas, 1903

Description

Hesperornis BW
Life restoration by Nobu Tamura, 2011.

Hesperornis was a large bird, reaching up to 1.8 metres (5.9 ft) in length.[2] It had virtually no wings, and swam with its powerful hind legs. Fossil evidence shows that the toes were probably lobed, as in today's grebes, rather than webbed as in those of loons.

Like many other Mesozoic birds such as Ichthyornis, Hesperornis had teeth as well as a beak, which were used to hold prey. In the hesperornithiform lineage they were of a different arrangement than in any other known bird (or in non-avian theropod dinosaurs), with the teeth sitting in a longitudinal groove rather than in individual sockets, in a notable case of convergent evolution with mosasaurs.[3][4] The teeth of Hesperornis were present along nearly the entire lower jaw (dentary) and the back of the upper jaw (maxilla). The front portion of the upper jaw (premaxilla) and tip of the lower jaw (predentary) lacked teeth and were probably covered in a beak. Studies of the bone surface show that at least the tips of the jaws supported a hard, keratinous beak similar to that found in modern birds.[5] The palate (mouth roof) contained small pits that allowed the lower teeth to lock into place when the jaws were closed.[6] 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.[2]

History

Hesperornis Regalis - Project Gutenberg eText 16474
Marsh's now-obsolete 1880 reconstruction of H. regalis.

The first Hesperornis specimen was discovered in 1871 by Othniel Charles Marsh. Marsh was undertaking his second western expedition, accompanied by ten students.[7] The team headed to Kansas where Marsh had dug before. Aside from finding more bones belonging to the flying reptile Pteranodon, Marsh discovered the skeleton of a "large fossil bird, at least five feet in height". The specimen was large, wingless, and had strong legs—Marsh considered it a diving species. Unfortunately, the specimen lacked a head.[8] Marsh named the find Hesperornis regalis, or "regal western bird".[9]

Marsh headed back west with a smaller party the following year. In western Kansas, one of Marsh's four students, Thomas H. Russell, discovered a "nearly perfect skeleton" of Hesperornis.[10] This specimen had enough of its head intact that Marsh could see that the creature's jaws had been lined with teeth.[11] Marsh saw important evolutionary implications of this find, along with Benjamin Mudge's find of the toothed bird Ichthyornis.[12] In an 1873 paper Marsh declared that "the fortunate discovery of these interesting fossils does much to break down the old distinction between Birds and Reptiles".[11] Meanwhile, Marsh's relationship with his rival Edward Drinker Cope soured further after Cope accidentally received boxes of fossils, including the toothed birds, that were meant for Marsh. Cope called the birds "simply delightful", but Marsh replied with accusations Cope had stolen the bones.[13] By 1873 their friendship dissolved into open hostility, helping to spark the Bone Wars. While Marsh would rarely go into the field after 1873, the collectors he paid continued to send him a stream of fossils. He eventually received parts of 50 specimens of Hesperornis, which allowed him to make a much stronger demonstration of an evolutionary link between reptiles and birds than had been possible before.[14]

Classification and Species

Hesperornis regalis fossil
H. regalis specimen at the AMNH

Many species have been described in this genus, though some are known from very few bones or even a single bone and cannot be properly compared with the more plentiful (but also incomplete) remains of other similar-sized taxa. In many cases, species have been separated by provenance, having been found in strata of different ages or in different locations, or by differences in size.

The first species to be described, the type species, is Hesperornis regalis. H. regalis is also the best known species, and dozens of specimens (from fragments to more complete skeletons) have been recovered, all from the Smoky Hill Chalk Member of the Niobrara Formation (dating to the early Campanian age, between 90–60 million years ago).[15] It is the only species of Hesperornis for which a nearly complete skull is known.

Hesperornis crassipes was named in 1876 by Marsh, who initially classified it in a different genus as Lestornis crassipes. H. crassipes was larger than H. regalis, had five ribs as opposed to four in the first species, and differed in aspects of the bone sculpturing on the breastbone and lower leg. H. crassipes is known from the same time and place as H. regalis. One incomplete skeleton is known, including teeth and parts of the skull.[16]

Hesperornis gracilis
Left leg of H. gracilis

Marsh explicitly named his second species of Hesperornis in 1876 for an incomplete metatarsus recovered from the same layers of the Niobrara chalk as H. regalis. He named this smaller species H. gracilis, and it was subsequently involved in the rather confused taxonomy of a specimen which would eventually form the basis of the new genus and species Parahesperornis alexi. The type specimen of P. alexi was assumed to belong to the same specimen as that of H. gracilis, so when Lucas (1903) decided that the former specimen represented a distinct genus, he mistakenly used the later specimen to anchor it, creating the name Hargeria gracilis. This mistake was rectified by later authors, who sank Hargeria back into Hesperornis and renamed the more distinctive specimen Parahesperornis.[17][18]

Coniornis
Type specimen (a partial right tibia) of H. altus in several views

The first species recognized from outside the Niobrara chalk, Hesperornis altus, lived about 78 million years ago in Montana, and is known from a partial lower leg from the base of the freshwater Judith River Formation (or, possibly, the top of the underlying, marine Claggett Shale formation). While initially placed in the new genus Coniornis by Marsh, this was due mostly to his belief that Hesperornis existed only in Kansas, so any species from Montana should be placed in a different genus. Most later researchers disagreed with this, and have placed Coniornis altus in the same genus as Hesperornis as H. altus.[19][20] A second species from Montana has also been described from the Claggett Shale. H. montana was named by Shufeldt in 1915, and while its known material (a single dorsal vertebra) cannot be directly compared to H. altus, Shufeldt and others have considered it distinct due to its apparently smaller size.[21]

In 1993, the first Hesperornis remains from outside of North America were recognized as a new species by Nessov and Yarkov. They named Hesperornis rossicus for a fragmentary skeleton from the early Campanian of Russia near Volgograd. Several other specimens from contemporary deposits have since been referred to this species. At about 1.4 metres (4.6 ft) long, H. rossicus was the largest species of Hesperornis and among the largest hesperornithines, slightly smaller than the large Canadian genus Canadaga.[9] Aside from its large size and different geographic location, H. rossicus differs from other Hesperornis in several features of the lower leg and foot, including a highly flattened metatarsus.[22]

In 2002, Martin and Lim formally recognized several new species for remains that had previously been unstudied or referred without consideration to previously named North American hesperornithines. These include the very small H. mengeli and H. macdonaldi, the slightly larger H. bairdi, and the very large H. chowi, all from the Sharon Springs member of the Pierre Shale Formation in South Dakota and Alberta, 80.5 million years ago.[23]

In addition, there are some unassigned remains, such as SGU 3442 Ve02 and LO 9067t and bones of an undetermined species from Tzimlyanskoe Reservoir near Rostov. The former two bones are probably H. rossicus; some remains assigned to that species in turn seem to belong to the latter undetermined taxon.[24]

Paleobiology

Hesperornis regalis
H. regalis skeleton in swimming pose; note feet pointing sideways

Hesperornis was primarily marine, and lived in the waters of such contemporary shallow shelf seas as the Western Interior Seaway, the Turgai Strait, and the North Sea,[24][25] which then were subtropical to tropical waters, much warmer than today. However, some of the youngest known specimens of Hesperornis have been found in inland freshwater deposits of the Foremost Formation, suggesting that some species of Hesperornis may have eventually moved, at least partially, away from a primarily marine habitat. Additionally, the species H. altus comes from the freshwater deposits at the base of the Judith River Formation.[26]

Tions and hip structure has borne out this comparison. In terms of limb length, shape of the hip bones, and position of the hip socket, Hesperornis is particularly similar to the common loon (Gavia immer), probably exhibiting a very similar manner of locomotion on land and in water. Like loons, Hesperornis were probably excellent foot-propelled divers, but ungainly on land.[27] Like loons, the legs were probably encased inside the body wall up to the ankle, causing the feet to jut out to the sides near the tail. This would have prevented them from bringing the legs underneath the body to stand, or under the center of gravity to walk. Instead, they likely moved on land by pushing themselves along on their bellies, like modern seals.[28]

Young Hesperornis grew fairly quickly and continuously to adulthood, as is the case in modern birds, but not Enantiornithes.[29]

Pathology

A Hesperornis leg bone uncovered in the 1960s was examined by David Burnham, Bruce Rothschild et al. and was found to bear bite marks from a young polycotylid plesiosaur (possibly a Dolichorhynchops or something similar). The Hesperornis's bone, specifically the condyle, shows signs of infection, indicating the bird survived the initial attack and escaped the predator. The discovery was published in the journal Cretaceous Research in 2016.[30]

References

  1. ^ Keiichi Aotsuka; Tamaki Sato (2016). "Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, Southern Manitoba, Canada". Cretaceous Research. in press: 154–169. doi:10.1016/j.cretres.2016.03.003.
  2. ^ a b Perrins, Christopher (1987) [1979]. Harrison, C.J.O. (ed.). Birds: Their Lifes, Their Ways, Their World. Pleasantville, NY, US: Reader's Digest Association, Inc. pp. 165–166. ISBN 0895770652.
  3. ^ Marsh, Othniel Charles (1880): Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
  4. ^ 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.
  5. ^ Heironymus, T.L.; Witmer, L.M. (2010). "Homology and evolution of avian compound rhamphothecae" (PDF). The Auk. 127 (3): 590–604. doi:10.1525/auk.2010.09122.
  6. ^ Elzanowski, A. (1991). "New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region". Postilla. 207: 1–20.
  7. ^ Thomson, 191.
  8. ^ Thomson, 193.
  9. ^ a b Holtz, Thomas R. Jr. (2011) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2010 Appendix.
  10. ^ Charles Schuchert and Clara Mae LeVene, O.C. Marsh: Pioneer in Paleontology, p. 427. New York: Arno Press, 1978. Later, Russell assisted Marsh while attending medical school; he became a surgeon, professor of Clinical Surgery in the Yale School of Medicine, and Marsh's personal physician until Marsh's death in 1899. See Proceedings of the Connecticut State Medical Society (Google eBook) and Genealogical and Family History of the State of Connecticut: A Record of the Achievements of Her People in the Making of a Commonwealth and the Founding of a Nation. Editorial staff: William Richard Cutter, Edward Henry Clement, Samuel Hart, Mary Kingsbury Talcott, Frederick Bostwick, Ezra Scollay Stearns. Volume I (of 4). New York: Lewis Historical Publishing Company, 1911.
  11. ^ a b Wallace, 86.
  12. ^ Thomson, 226.
  13. ^ Wallace, 87.
  14. ^ Wallace, 132.
  15. ^ Carpenter, K. (2003). Harries, P. J (ed.). "Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale)". High-Resolution Approaches in Stratigraphic Paleontology. Topics in Geobiology. 21: 421–437. doi:10.1007/978-1-4020-9053-0. ISBN 978-1-4020-1443-7.
  16. ^ Marsh, O.C. (1876). "Notice of new Odontornithes". The American Journal of Science and Arts. 11 (66): 509–511. doi:10.2475/ajs.s3-11.66.509.
  17. ^ Bell, A.; Everhart, M.J. (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. doi:10.1660/062.112.0202.
  18. ^ Mortimer, Michael (2004): The Theropod Database: Phylogeny of taxa Archived 2013-05-16 at the Wayback Machine.
  19. ^ Shufeldt, R.W. (1915). "Fossil birds in the Marsh Collection of Yale University". Transactions of the Connecticut Academy of Arts and Sciences. 19: 1–110.
  20. ^ Martin, L.D. (1984). "A new hesperornithid and the relationships of the Mesozoic birds". Transactions of the Kansas Academy of Science. 87 (3/4): 141–150. doi:10.2307/3627850. JSTOR 3627850.
  21. ^ Shufeldt, R.W. (1915). "The fossil remains of a species of Hesperornis found in Montana". The Auk. 32 (3): 290–294. doi:10.2307/4072679. JSTOR 4072679.
  22. ^ Kurochkin, (2000). "Mesozoic birds of Mongolia and the former USSR." Pp. 533–559 in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia.
  23. ^ Martin, L. and Lim, (2002). "New information on the hesperornithiform radiation." pp. 113–124 in Zhou and Zhang (eds.), Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing.
  24. ^ a b Rees, Jan & Lindgren, Johan; Lindgren (2005). "Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms". Palaeontology. 48 (6): 1321–1329. doi:10.1111/j.1475-4983.2005.00507.x.CS1 maint: multiple names: authors list (link)
  25. ^ Hills, L. V.; Nicholls, E. L.; Núñez-Betelu, L. "Koldo" M.; McIntyre, D. J. (1999). "Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities". Canadian Journal of Earth Sciences. 36 (9): 1583–1588. doi:10.1139/e99-060. Archived from the original on 2007-03-11.
  26. ^ Fox, R.C. (1974). "A middle Campanian, nonmarine occurrence of the Cretaceous toothed bird Hesperornis Marsh". Canadian Journal of Earth Sciences. 11 (9): 1335–1338. doi:10.1139/e74-127.
  27. ^ Reynaud, F. (2006). "Hind limb and pelvis proportions of Hesperornis regalis: A comparison with extant diving birds". Journal of Vertebrate Paleontology. 26 (3): 115A. doi:10.1080/02724634.2006.10010069.
  28. ^ 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 (1): 59–63. doi:10.1016/j.palwor.2012.02.005.
  29. ^ Chinsamy A, Martin, Larry D. & Dobson, P.; Martin; Dobson (1998). "Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas". Cretaceous Research. 19 (2): 225–235. doi:10.1006/cres.1997.0102.CS1 maint: multiple names: authors list (link)
  30. ^ http://www.bbc.com/earth/story/20160311-how-a-bird-managed-to-escape-a-predatory-sea-monster?ocid=ww.social.link.facebook

Sources

  • Thomson, Keith Stewart (2008). The Legacy of the Mastodon: The Golden Age of Fossils in America. Yale University Press. ISBN 978-0-300-11704-2.
  • Wallace, David Rains (1999). The Bonehunters' Revenge: Dinosaurs, Greed, and the Greatest Scientific Feud of the Gilded Age. Houghton Mifflin Books. ISBN 0-618-08240-9.

Further reading

External links

Asiahesperornis

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.

Baptornis

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.

Canadaga

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.

Foremost Formation

The Foremost Formation is a stratigraphic unit of Late Cretaceous (Campanian) age that underlies much of southern Alberta, Canada. It was named for outcrops in Chin Coulee near the town of Foremost and is known primarily for its dinosaur remains and other fossils.

Gansus

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

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

Hesperornithes

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.

Ichthyornis

Ichthyornis (meaning "fish bird", after its fish-like vertebrae) is an extinct genus of toothed seabird-like ornithuran from the late Cretaceous period of North America. Its fossil remains are known from the chalks of Alberta, Alabama, Kansas (Greenhorn Limestone), New Mexico, Saskatchewan, and Texas, in strata that were laid down in the Western Interior Seaway during the Turonian through Campanian ages, about 95–83.5 million years ago. Ichthyornis is a common component of the Niobrara Formation fauna, and numerous specimens have been found.

Ichthyornis has been historically important in shedding light on bird evolution. It was the first known prehistoric bird relative preserved with teeth, and Charles Darwin noted its significance during the early years of the theory of evolution. Ichthyornis remains important today as it is one of the few Mesozoic era ornithurans known from more than a few specimens.

Judith River Formation

The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age. It was laid down during the same time period as portions of the Two Medicine Formation of Montana and the Oldman Formation of Alberta.

It is an historically important formation, explored by early American paleontologists such as Edward Drinker Cope, who named several dinosaurs from scrappy remains found here on his 1876 expedition (such as Monoclonius). Modern work has found nearly complete skeletons of the hadrosaurid Brachylophosaurus.

List of creatures in Primeval

The following is a complete list of creatures from the universe of ITV science fiction television series Primeval and also any spin-off media, including Primeval: New World ("PNW"). The series includes various imaginary species which are not native to the series setting, with some being prehistoric and others being futuristic. Various creatures were designed with some artistic license, for dramatic effect. A number of creatures from the Walking with... series were also reimagined for dramatic effect.

In 2007 Character Options announced they would create Primeval action figures, including both a flying Rex and a large plush toy Rex, Future Predators, Hesperornis and dodos.

List of the Mesozoic life of Kansas

This list of the Mesozoic life of Kansas contains the various prehistoric life-forms whose fossilized remains have been reported from within the US state of Kansas and are between 252.17 and 66 million years of age.

Odontornithes

Odontornithes is an obsolete and disused taxonomic term proposed by Othniel Charles Marsh for birds possessing teeth, notably the genera Hesperornis and Ichthyornis from the Cretaceous deposits of Kansas.In 1875 Marsh divided this "subclass" into Odontolcae, with the teeth standing in grooves, and Odontotormae, with the teeth in separate alveoles or sockets. In his 1880 work, Odontornithes: A monograph on the extinct toothed birds of North America, he added the Saururae, represented by Archaeopteryx, as a third order.The resulting classification was paraphyletic, not accurately resolving evolutionary relationships, and so it has been abandoned by most modern scientists, though at least one 21st century paper re-used the concept under the older name Odontoholomorphae (first coined by Stejneger, 1885).Étienne Geoffroy Saint-Hilaire stated in 1821 that he had found a considerable number of tooth buds in the upper and lower jaws of the Palaeornis torquatus (rose-ringed parakeet). Émile Blanchard felt justified in recognizing flakes of dentine. However, M. Braun and especially P. Fraisse showed later that the structures in question are of the same kind as the well-known serrated "teeth" of the bill of anserine birds. In fact the papillae observed in the embryonic birds are the soft cutaneous extensions into the surrounding horny sheath of the bill, comparable to the well-known nutritive papillae in a horse's hoof. They are easily exposed in the well-macerated under jaw of a parrot, after removal of the horny sheath. Occasionally calcification occurs in or around these papillae, as it does regularly in the egg tooth of the embryos of all birds.The best known of the "Odontornithes" are Hesperornis regalis, standing about 3 ft. high, the somewhat taller H. crassipes, and Ichthyornis dispar. Hesperornis looked somewhat similar to a loon, while Ichthyornis was quite similar to a gull or petrel. However, they were entirely distinct groups of birds and merely shared with modern birds some distant ancestry in the Early Cretaceous. The Hesperornis lineage may have derived even sooner or possibly independently from the ancestors of modern birds.

Ornithurae

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.

Paleornithology

Paleornithology also known as Avian Paleontology is the scientific study of bird evolution and fossil birds. It is a mix of ornithology and paleontology. Paleornithology began with the discovery of Archaeopteryx. The reptilian relationship of birds and their ancestors, the theropod dinosaurs, are important aspects of paleornithological research. Other areas of interest to paleornithologists are the early sea-birds Ichthyornis, Hesperornis, and others. Notable paleornithologists are Storrs L. Olson, Alexander Wetmore, Alan Feduccia, Cécile Mourer-Chauviré, Philip Ashmole, Pierce Brodkorb, Trevor H. Worthy, Zhou Zhonghe, Yevgeny Kurochkin, Bradley C. Livezey, Gareth J. Dyke, Luis M. Chiappe, Gerald Mayr and David Steadman.

Parahesperornis

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.

Patagopterygiformes

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

Protostega

Protostega ('first roof') is an extinct genus of sea turtle containing a single species, Protostega gigas. Its fossil remains have been found in the Smoky Hill Chalk formation of western Kansas (Hesperornis zone, dated to 83.5 million years ago) and time-equivalent beds of the Mooreville Chalk Formation of Alabama. Fossil specimens of this species were first collected in 1871, and named by Edward Drinker Cope in 1872. With a length of 3 metres (9.8 ft), it is the second-largest sea turtle that ever lived, second only to the giant Archelon, and the third-largest turtle of all time behind Archelon and Stupendemys.

Smoky Hill Chalk

The Smoky Hill Chalk Member of the Niobrara Chalk formation is a Cretaceous conservation Lagerstätte, or fossil rich geological formation, known primarily for its exceptionally well-preserved marine reptiles. The Smoky Hill Chalk Member is the uppermost of the two structural units of the Niobrara Chalk. It is underlain by the Fort Hays Limestone Member; and the Pierre Shale overlies the Smoky Hill Chalk. The Smoky Hill Chalk outcrops in parts of northwest Kansas, its most famous localities for fossils, and in southeastern Nebraska. Large well-known fossils excavated from the Smoky Hill Chalk include marine reptiles such as plesiosaurs, large bony fish such as Xiphactinus, mosasaurs, flying reptiles or pterosaurs (namely Pteranodon), flightless marine birds such as Hesperornis, and turtles. Many of the most well-known specimens of the marine reptiles were collected by dinosaur hunter Charles H. Sternberg and his son George. The son collected a unique fossil of the giant bony fish Xiphactinus audax with the skeleton of another bony fish, Gillicus arcuatus inside the larger one. Another excellent skeleton of Xiphactinus audax was collected by Edward Drinker Cope during the late nineteenth century heyday of American paleontology and its Bone Wars.

Tingmiatornis

Tingmiatornis (meaning "bird that flies") is a genus of flighted and possibly diving ornithurine bird from the High Arctic of Canada. The genus contains a single species, T. arctica, described in 2016, which lived during the Turonian epoch of the Cretaceous.

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