Caudipteryx

Caudipteryx (which means "tail feather") is a genus of peacock-sized theropod dinosaurs that lived in the Aptian age of the early Cretaceous Period (about 124.6 million years ago). They were feathered and remarkably birdlike in their overall appearance.[1] Two species have been described; C. zoui (the type species), in 1998,[1] and C. dongi, in 2000.[2]

Caudipteryx fossils were first discovered in the Yixian Formation of the Sihetun area of Liaoning Province, northeastern China in 1997.

Caudipteryx
Temporal range: Early Cretaceous, 124.6 Ma
Caudipteryx zoui - Untere Kreide - Liaoning-China
Mounted C. zoui skeleton restoration
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Caudipteridae
Genus: Caudipteryx
Ji et al., 1998
Type species
Caudipteryx zoui
Ji et al., 1998
Species
  • C. zoui Ji et al., 1998
  • C. dongi Zhou & Wang, 2000

Description

Caudipteryx Scale
Size comparison of Caudipteryx species to a human.

Caudipteryx, like many other maniraptorans, has an interesting mix of reptile- and bird-like anatomical features.[3]

Protarchaeopteryx at the Geological Museum of China
Caudipteryx holotype NGMC 97 4 A at the Geological Museum of China

Caudipteryx had a short, boxy skull with a beak-like snout that retained only a few tapered teeth in the front of the upper jaw. It had a stout trunk, long legs and was probably a swift runner.

Caudipteryx has a short tail stiffened toward the tip, with few vertebrae, like in birds and other oviraptorosaurs. It has a primitive pelvis and shoulder, and primitive skull details in the quadratojugal, squamosal, quadrate, jugal, and mandibular fenestra (in the cheek, jaw, and jaw joint). It has a hand skeleton with a reduced third finger, like that of primitive birds and the oviraptorid Ingenia.[4]

Caudipteryx had uncinate processes on the ribs, birdlike teeth, a first toe which may or may not be partially reversed and overall body proportions that are comparable to those of modern flightless birds.[1][2][3][5][6]

Paleobiology

Feathers

Caudipteryx2mmartyniuk
Restoration of C. zoui

The hands of Caudipteryx supported symmetrical, pennaceous feathers that had vanes and barbs, and that measured between 15–20 centimetres (5.9–7.9 inches) long. These primary feathers were arranged in a wing-like fan along the second finger, just like primary feathers of birds and other maniraptorans. No fossil of Caudipteryx zoui preserves any secondary feathers attached to the forearms, as found in dromaeosaurids, Archaeopteryx and modern birds.[3] Either these arm feathers are not preserved, or they were not present on Caudipteryx in life. An additional fan of feathers existed on its short tail. The shortness and symmetry of the feathers, and the shortness of the arms relative to the body size, indicate that Caudipteryx was flightless.

The body was covered in a coat of short, simple, down-like feathers.

Diet

Caudipteryx zoui
C. zoui holotype with feather impressions and stomach content

Caudipteryx is thought to have been an omnivore. In at least two specimens of Caudipteryx (NGMC 97 4 A and NGMC 97 9 A), gastroliths are preserved. As in some herbivorous dinosaurs, the avialan Sapeornis, and modern birds, these gastroliths remain in the position where the animals' gizzards would have been.[1]

Paleoecology

All Caudipteryx fossils were recovered from the Yixian Formation in Liaoning, China. Specifically, they come from a small area of the Jianshangou bed, near the town of Zhangjiakou. They appear to have been fairly common, though isolated to this small region. The specific region in which Caudipteryx lived was home to the other feathered dinosaurs Dilong and Sinornithosaurus.[7]

Implications

Caudipteryx zoui, feathered dinosaur plate, Early Cretaceous, Yixian Formation, Liaoning, China - Houston Museum of Natural Science - DSC01866
Cast of a C. zoui specimen, Houston Museum of Natural Science

The discovery of Caudipteryx led to many intensive studies on and debate over the relationship of birds and dinosaurs. The possible positions in the debate can be summarized as follows: Caudipteryx is either a member of the Oviraptorosauria, or a bird, or both, and birds are either dinosaurs or they are not. (See the rest of this section and Phylogeny, below).

Because Caudipteryx has clear and unambiguously pennaceous feathers, like modern birds, and because several cladistic analyses have consistently recovered it as a nonavian, oviraptorid, dinosaur, it provided, at the time of its description, the clearest and most succinct evidence that birds evolved from dinosaurs. Lawrence Witmer stated: “The presence of unambiguous feathers in an unambiguously nonavian theropod has the rhetorical impact of an atomic bomb, rendering any doubt about the theropod relationships of birds ludicrous.”[3]

However, not all scientists agreed that Caudipteryx was unambiguously non-avian, and some of them continued to doubt that general consensus. Paleornithologist Alan Feduccia sees Caudipteryx as a flightless bird evolving from earlier archosaurian dinosaurs rather than from late theropods.[8] Jones et al. (2000) found that Caudipteryx was a bird based on a mathematical comparison of the body proportions of flightless birds and non-avian theropods. Dyke and Norell (2005) criticized this result for flaws in their mathematical methods, and produced results of their own which supported the opposite conclusion.[6][9]

Other researchers not normally involved in the debate over bird origins, such as Zhou, acknowledged that the true affinities of Caudipteryx were debatable.[5]

Classification

Caudipteryx
Skeletal restorations of three specimens

The consensus view, based on several cladistic analyses, is that Caudipteryx is a basal (primitive) member of the Oviraptoridae, and the oviraptorids are nonavian theropod dinosaurs.[9] Incisivosaurus is the only oviraptorid that is more primitive.[10]

Halszka Osmólska et al. (2004) ran a cladistic analysis that came to a different conclusion. They found that the most birdlike features of oviraptorids actually place the whole clade within Aves itself, meaning that Caudipteryx is both an oviraptorid and a bird. In their analysis, birds evolved from more primitive theropods, and one lineage of birds became flightless, re-evolved some primitive features, and gave rise to the oviraptorids. This analysis was persuasive enough to be included in paleontological textbooks like Benton's Vertebrate Paleontology (2005).[11] The view that Caudipteryx was secondarily flightless is also preferred by Gregory S. Paul,[12] et al.,[13] and Maryańska et al.[14]

Others, such as Stephen Czerkas and Larry Martin have concluded that Caudipteryx is not a theropod dinosaur at all.[15] They believe that Caudipteryx, like all maniraptorans, is a flightless bird, and that birds evolved from non-dinosaurian archosaurs.[16]

See also

References

  1. ^ a b c d Ji, Q.; Currie, P.J.; Norell, M.A.; Ji, S. (1998). "Two feathered dinosaurs from northeastern China" (PDF). Nature. 393 (6687): 753–761. Bibcode:1998Natur.393..753Q. doi:10.1038/31635. Archived from the original (PDF) on 2008-12-17.
  2. ^ a b Zhou, Z.; Wang, X. (2000). "A new species of Caudipteryx from the Yixian Formation of Liaoning, northeast China" (PDF). Vertebrata PalAsiatica. 38 (2): 113–130. Archived from the original (PDF) on 2007-10-07.
  3. ^ a b c d Witmer, L.M. (2005). “The Debate on Avian Ancestry; Phylogeny, Function and Fossils”, Mesozoic Birds: Above the Heads of Dinosaurs : 3–30. ISBN 0-520-20094-2
  4. ^ Osmolska, H., Currie, P.J., and Barsbold, R. (2004). "Oviraptorosauria." In Weishampel, Dodson, Osmolska (eds.) The Dinosauria, second edition. University of California Press, 2004.
  5. ^ a b Zhou, Z.; Wang, X.; Zhang, F.; Xu, X. (2000). "Important features of Caudipteryx - Evidence from two nearly complete new specimens" (PDF). Vertebrata PalAsiatica. 38 (4): 241–254.
  6. ^ a b Jones, T.D.; Farlow, J.O.; Ruben, J.A.; Henderson, D.M.; Hillenius, W.J. (2000). "Cursoriality in bipedal archosaurs". Nature. 406 (6797): 716–718. doi:10.1038/35021041. PMID 10963594. PDF Supplementary information
  7. ^ Xu, X.; Norell, M.A. (2006). "Non-Avian dinosaur fossils from the Lower Cretaceous Jehol Group of western Liaoning, China". Geological Journal. 41 (3–4): 419–437. doi:10.1002/gj.1044.
  8. ^ Feduccia, A. (1999). The Origin and Evolution of Birds. 420 pp. Yale University Press, New Haven. ISBN 0-300-07861-7.
  9. ^ a b Dyke, Gareth J.; Norell, Mark A. (2005). "Caudipteryx as a non-avialan theropod rather than a flightless bird" (PDF). Acta Palaeontologica Polonica. 50 (1): 101–116.
  10. ^ Turner, Alan H.; Pol, Diego; Clarke, Julia A.; Erickson, Gregory M.; Norell, Mark (2007). "A basal dromaeosaurid and size evolution preceding avian flight" (PDF). Science. 317 (5843): 1378–1381. Bibcode:2007Sci...317.1378T. doi:10.1126/science.1144066. PMID 17823350.
  11. ^ Osmólska, Halszka, Currie, Philip J., Barsbold, Rinchen (2004) The Dinosauria Weishampel, Dodson, Osmolska. "Chapter 8 Oviraptorosauria" University of California Press.
  12. ^ Paul, G.S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press, Baltimore. ISBN 0-8018-6763-0
  13. ^ Lü, J., Dong, Z., Azuma, Y., Barsbold, R., and Tomida, Y. (2002). "Oviraptorosaurs compared to birds." In Zhou, Z., and Zhang, F. (eds.), Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, 175–189. Beijing Science Press.
  14. ^ Maryańska, T.; Osmólska, H.; Wolsan, M. (2002). "Avialan status for Oviraptorosauria" (PDF). Acta Palaeontologica Polonica. 47 (1): 97–116.
  15. ^ Martin, Larry D. (2004). "A basal archosaurian origin for birds". Acta Zoologica Sinica. 50 (6): 978–990.
  16. ^ Martin, L.D.; Czerkas, S.A. (2000). "The Fossil Record of Feather Evolution in the Mesozoic" (PDF). American Zoologist. 40 (4): 687–694. doi:10.1668/0003-1569(2000)040[0687:TFROFE]2.0.CO;2.

External links

1998 in paleontology

Paleontology or palaeontology (from Greek: paleo, "ancient"; ontos, "being"; and logos, "knowledge") is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1998.

Barremian

The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch (or Lower Cretaceous series). It is preceded by the Hauterivian and followed by the Aptian stage.

Caenagnathoidea

Caenagnathoidea ("recent jaw forms") is a group of advanced oviraptorosaurian dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, often with bony crests atop the head. They ranged in size from Caudipteryx, which was the size of a turkey, to the 8 meter long, 1.4 ton Gigantoraptor. The group (along with all maniraptoran dinosaurs) is close to the ancestry of birds. The most complete specimens have been found in Asia, representing members of the sub-group Oviraptorinae. Notable but fragmentary remains are also known from North America, almost all of which belong to the subgroup Elmisaurinae.The earliest definitive caenangnathoid is Microvenator celer, which dates to the late Aptian age of the early Cretaceous period, though the slightly earlier Caudipteryx from the lower Yixian Formation of China, may also be a member of this group.

Caudipteridae

Caudipteridae is a family of oviraptorosaurian dinosaurs known from the Early Cretaceous of China. Found in the Yixian and Jiufotang Formations, the group existed between 125-120 million years ago. Distinguishing characteristics of this group have been indicated as including a unique dagger-shaped pygostyle (the bone at the tip of the tail in birds, used to anchor a "fan" of feathers). No clade definition has been given.

The first caudipterid described was Caudipteryx zoui (named in 1998), though the family itself was not named until the discovery of a second species, Caudipteryx dongi, in 2000. Caudipteridae was restricted to the single genus Caudipteryx and was therefore monotypic, containing only a single type and often considered redundant. However, in 2008 Similicaudipteryx yixianensis was described and classified as a caudipterid.

Dinosaur coloration

Dinosaur color is one of the unknowns in the field of paleontology as skin pigmentation is nearly always lost during the fossilization process. However, recent studies of feathered dinosaurs have shown that we might be able to infer the color of some species through the use of melanosomes, the color-determining pigments within the feathers.

Gigantoraptor

Gigantoraptor is a genus of giant oviraptorosaurian theropod dinosaur.

Grallator

Grallator ["GRA-luh-tor"] is an ichnogenus (form taxon based on footprints) which covers a common type of small, three-toed print made by a variety of bipedal theropod dinosaurs. Grallator-type footprints have been found in formations dating from the Early Triassic through to the early Cretaceous periods. They are found in the United States, Canada, Europe, Australia, Brazil (Sousa and Santa Maria Formations) and China, but are most abundant on the east coast of North America, especially the Triassic and Early Jurassic formations of the northern part of the Newark Supergroup. The name Grallator translates into "stilt walker", although the actual length and form of the trackmaking legs varied by species, usually unidentified. The related term "Grallae" is an ancient name for the presumed group of long-legged wading birds, such as storks and herons. These footprints were given this name by their discoverer, Edward Hitchcock, in 1858.Grallator footprints are characteristically three-toed (tridactyl) and range from 10 to 20 centimeters (or 4 to 8 inches) long. Though the tracks show only three toes, the trackmakers likely had between four and five toes on their feet. While it is usually impossible to match these prints with the exact dinosaur species that left them, it is sometimes possible to narrow down potential trackmakers by comparing the proportions in individual Grallator ichnospecies with known dinosaurs of the same formation. For example, Grallator tracks identified from the Yixian Formation may have been left by Caudipteryx.

Incisivosaurus

Incisivosaurus ("incisor lizard") is a genus of small, probably herbivorous theropod dinosaur from the early Cretaceous Period of what is now the People's Republic of China. The first specimen to be described (by Xu et al. in 2002), IVPP V13326, is a skull that was collected from the lowermost levels (the fluvial Lujiatun beds) of the Yixian Formation (dating to the Barremian stage about 126 million years ago in the Sihetun area, near Beipiao City, in western Liaoning Province. The most significant, and highly unusual, characteristic of this dinosaur is its apparent adaptation to an herbivorous or omnivorous lifestyle. It was named for its prominent, rodent-like front teeth, which show wear patterns commonly found in plant-eating dinosaurs. The specific name gauthieri honors Dr. Jacques Gauthier, a pioneer of the phylogenetic method of classification.

Larry Martin

Larry Dean Martin (December 8, 1943 – March 9, 2013) was an American vertebrate paleontologist and curator of the Natural History Museum and Biodiversity Research Center at the University of Kansas. Among Martin's work is research on the Triassic reptile Longisquama and theropod dinosaur (or fossil bird) Caudipteryx and Dakotaraptor. According to the University of Kansas, he "has been a leading opponent of the theory that birds are 'living dinosaurs.'"

He has also appeared in a few television documentaries about dinosaurs, including Jurassic Fight Club.

He died of cancer at the age of 69 on March 9, 2013, after a long battle with the disease.

List of non-avian dinosaur species preserved with evidence of feathers

Several non-avian dinosaurs were feathered. Direct evidence of feathers exists for the following species, listed in the order currently accepted evidence was first published. In all examples, the evidence described consists of feather impressions, except those genera inferred to have had feathers based on skeletal or chemical evidence, such as the presence of quill knobs (the anchor points for wing feathers on the forelimb) or a pygostyle (the fused vertebrae at the tail tip which often supports large feathers).

Ostromia crassipes (1970)

Avimimus portentosus (inferred 1987: ulnar ridge)

Sinosauropteryx prima (1996)

Fulicopus lyellii, an ichnotaxon, possible squatting Dilophosaurus or similar. (1996)

Protarchaeopteryx robusta (1997)

GMV 2124 (1997)

Caudipteryx zoui (1998)

Rahonavis ostromi (inferred 1998: quill knobs; possibly avialan)

Shuvuuia deserti (1999)

Beipiaosaurus inexpectus (1999)

Sinornithosaurus millenii (1999)

Caudipteryx dongi (2000)

Caudipteryx sp. (2000)

Microraptor zhaoianus (2000)

Nomingia gobiensis (inferred 2000: pygostyle)

Psittacosaurus sp.? (2002)

Scansoriopteryx heilmanni (2002; possibly avialan)

Yixianosaurus longimanus (2003)

Dilong paradoxus (2004)

Pedopenna daohugouensis (2005; possibly avialan)

Jinfengopteryx elegans (2005)

Juravenator starki (2006)

Sinocalliopteryx gigas (2007)

Velociraptor mongoliensis (inferred 2007: quill knobs)

Epidexipteryx hui (2008; possibly avialan)

Similicaudipteryx yixianensis (inferred 2008: pygostyle; confirmed 2010)

Anchiornis huxleyi (2009; possibly avialan)

Tianyulong confuciusi? (2009)

Concavenator corcovatus? (inferred 2010: quill knobs?)

Xiaotingia zhengi (2011; possibly avialan)

Yutyrannus huali (2012)

Sciurumimus albersdoerferi (2012)

Ornithomimus edmontonicus (2012)

Ningyuansaurus wangi (2012)

Eosinopteryx brevipenna (2013; possibly avialan)

Jianchangosaurus yixianensis (2013)

Aurornis xui (2013; possibly avialan)

Changyuraptor yangi (2014)

Kulindadromeus zabaikalicus? (2014)

Citipati osmolskae (inferred 2014: pygostyle)

Conchoraptor gracilis (inferred 2014: pygostyle)

Deinocheirus mirificus? (inferred 2014: pygostyle)

Yi qi (2015)

Ornithomimus sp. (2015)

Zhenyuanlong suni (2015)

Dakotaraptor steini (inferred 2015: quill knobs)

Apatoraptor pennatus (inferred 2016: quill knobs)

Jianianhualong tengi (2017)

Serikornis sungei (2017)

Caihong juji (2018)Note that the filamentous structures in some ornithischian dinosaurs (Psittacosaurus, Tianyulong and Kulindadromeus) and the pycnofibres found in some pterosaurs may or may not be homologous with the feathers of theropods.

Ningyuansaurus

Ningyuansaurus is a basal oviraptorosaurian dinosaur genus. It contains the single species Ningyuansaurus wangi, known from a fossil specimen from the Early Cretaceous Yixian Formation (Aptian stage, 124.6 Ma ago) of Jianchang, western Liaoning Province, People's Republic of China. It is thought to be the basalmost species of oviraptorosaur, based on its long skull and a greater number of teeth in comparison to any other known oviraptorosaur. The generic name Ningyuansaurus is derived from Ningyuan, an ancient name for Xingcheng City. The specific name honors Wang Qiuwu, the private owner of the specimen who donated it for scientific study. The specimen is currently housed in the Confuciusornis Museum in Xingcheng.

Nomingia

Nomingia is a genus of oviraptorid theropod dinosaur hailing from the Late Cretaceous Bugin Tsav Beds of Mongolia.

Oviraptor

Oviraptor is a genus of small Mongolian theropod dinosaurs, first discovered by technician George Olsen in an expedition led by Roy Chapman Andrews, and first described by Henry Fairfield Osborn, in 1924. Its name is Latin for 'egg taker' or "egg seizer", referring to the fact that the first fossil specimen was discovered atop a pile of what were thought to be Protoceratops eggs, and the specific name philoceratops means "lover of ceratopsians", also given as a result of this find. In his 1924 paper, Osborn explained that the name was given due to the close proximity of the skull of Oviraptor to the nest (it was separated from the eggs by only 4 inches or 10 centimetres of sand). However, Osborn also suggested that the name Oviraptor "may entirely mislead us as to its feeding habits and belie its character". In the 1990s, the discovery of nesting oviraptorids like Citipati proved that Osborn was correct in his caution regarding the name. These finds showed that the eggs in question probably belonged to Oviraptor itself, and that the specimen was actually brooding its eggs, when it died at the nest.

Oviraptor lived in the late Cretaceous period, during the late Campanian stage about 75 million years ago; only one definitive specimen is known (with associated eggs), from the Djadokhta Formation of Mongolia, though a possible second specimen (also with eggs) comes from the northeast region of Inner Mongolia, China, in an area called Bayan Mandahu.

Oviraptorosauria

Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or without bony crests atop the head. They ranged in size from Caudipteryx, which was the size of a turkey, to the 8-metre-long, 1.4-ton Gigantoraptor. The group (along with all maniraptoran dinosaurs) is close to the ancestry of birds. Analyses like those of Maryanska et al (2002) and Osmólska et al. (2004) suggest that they may represent primitive flightless birds. The most complete oviraptorosaur specimens have been found in Asia. The North American oviraptorosaur record is sparse.The earliest and most basal ("primitive") known oviraptorosaurs are Ningyuansaurus wangi, Protarchaeopteryx robusta and Incisivosaurus gauthieri, both from the lower Yixian Formation of China, dating to about 125 million years ago during the Aptian age of the early Cretaceous period. A tiny neck vertebra reported from the Wadhurst Clay Formation of England shares some features in common with oviraptorosaurs, and may represent an earlier occurrence of this group (at about 140 million years ago).

Similicaudipteryx

Similicaudipteryx, meaning "similar to Caudipteryx" (which itself means "tail feather"), is a genus of theropod dinosaur of the family Caudipteridae.

Timeline of dromaeosaurid research

This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like Velociraptor. Since the Native Americans of Montana used the sediments of the Cloverly Formation to produce pigments, they may have encountered remains of the dromaeosaurid Deinonychus hundreds of years before these fossils came to the attention of formally trained scientists.In 1922 Matthew and Brown named the new genus and species Dromaeosaurus albertensis, considering it a new type within the family Deinodontidae, a now defunct family name that once applied to the tyrannosaurs. Not long after, Velociraptor was discovered in Mongolia by the Central Asiatic Expedition. Dromaeosaur research was fairly quiet until the 1960s, when John Ostrom described the new genus and species Deinonychus antirrhopus. This discovery played a major role in setting off the Dinosaur Renaissance because Deinonychus was obviously a vigorous, active animal, and exhibited characteristics linking it to the origin of birds. As such it brought support for controversial reinterpretations of dinosaurs as warm-blooded and ancestral to birds. Its distinct nature and similarity to Dromaeosaurus led Ostrom to follow Edwin Colbert and Dale Russel's suggestion that the Dromaeosaurinae be regarded as its own family separate from the Deinodontidae.After Ostrom's initial research on Deinonychus, evidence continued to mount for a close evolutionary relationship between dromaeosaurids and birds. The dromaeosaurid Sinornithosaurus milennii, described in 1999 by Xu, Wang, and Wu, is a notable example as the fine-grained Chinese limestone from which it was collected preserved its life covering of feathers. Discoveries of feathered dromaeosaurids continued into the 2000s. Xu, Zhou, and Wang named the new genus Microraptor in 2000. Three years later, Xu and others would report a new species in this genus that exhibited a bizarre "four winged" body plan with long pennaceous flight feathers on both its front and hind limbs.

Timeline of oviraptorosaur research

This timeline of oviraptorosaur research is a chronological listing of events in the history of paleontology focused on the oviraptorosaurs, a group of beaked, bird-like theropod dinosaurs. The early history of oviraptorosaur paleontology is characterized by taxonomic confusion due to the unusual characteristics of these dinosaurs. When initially described in 1924 Oviraptor itself was thought to be a member of the Ornithomimidae, popularly known as the "ostrich" dinosaurs, because both taxa share toothless beaks. Early caenagnathid oviraptorosaur discoveries like Caenagnathus itself were also incorrectly classified at the time, having been misidentified as birds.The hypothesis that caenagnathids were birds was questioned as early as 1956 by Romer, but not corrected until Osmolska formally reclassified them as dinosaurs in 1976. Meanwhile, the classification of Oviraptor as an ornithomimid persisted unquestioned by researchers like Romer and Steel until the early 1970s when Dale Russell argued against the idea in 1972. In 1976 when Osmolska recognized Oviraptor's relationship with the Caenagnathids, she also recognized that it was not an ornithomimid and reclassified it as a member of the former family. However, that same year Rinchen Barsbold argued that Oviraptor belonged to a distinct family he named the Oviraptoridae and he also formally named the Oviraptorosauria later in the same year.Like their classification, the paleobiology of oviraptorosaurs has been subject to controversy and reinterpretation. The first scientifically documented Oviraptor skeleton was found lying on a nest of eggs. Because its powerful parrot-like beak appeared well-adapted to crushing hard food items and the eggs were thought to belonged to the neoceratopsian Protoceratops, oviraptorosaurs were thought to be nest-raiders that preyed on the eggs of other dinosaurs. In the 1980s, Barsbold proposed that oviraptorosaurs used their beaks to crack mollusk shells as well. In 1993, Currie and colleagues hypothesized that small vertebrate prey may have also been part of the oviraptorosaur diet. Not long after, fossil embryonic remains cast doubt on the popular reconstruction of oviraptorosaurs as egg thieves when it was discovered that the "Protoceratops" eggs that Oviraptor was thought to be "stealing" actually belonged to Oviraptor itself. The discovery of additional Oviraptor preserved on top of nests in lifelike brooding posture firmly established that oviraptorosaurs had been "framed" as egg thieves and were actually caring parents incubating their own nests.

Uncinate processes of ribs

The uncinate processes of the ribs are extensions of bone that project caudally from the vertical segment of each rib. (Uncinate means hooked from Latin uncinatus, from uncinus, barb, from uncus, hook.) They are found in birds (except for screamers), reptiles, and the early amphibian Ichthyostega.These processes can serve to attach scapula muscles, and help to strengthen the rib cage overlapping with the rib behind them. They are also shown to have a role in respiration by increasing the effectiveness of muscles involved in inspiration including the appendicocostal muscles. The processes are short in walking birds and long in diving species and are of intermediate length in non-specialist birds. The screamers (Anhimidae) are unique in lacking this process. The process has also been noted in some enantiornitheans. Although among living vertebrates, bony uncinate processes are unique to birds, cartilaginous uncinate processes are present in crocodiles. The uncinate process has also been reported in fossil vertebrates including Sphenodon, Caudipteryx, oviraptorids, Confuciusornis, Chaoyangia, and Longipteryx; however it does not occur in Archaeopteryx.

Wing-assisted incline running

Wing-assisted incline running (abbreviated as "WAIR") is a running behavior observed in living birds as well as a model proposed to explain the evolution of avian flight. WAIR allows birds to run up steep or vertical inclines by flapping their wings, scaling greater inclines than possible through running alone. The WAIR origin-of-flight hypothesis proposes that the nascent wings of theropod dinosaurs were used to propel the animal up slopes, such as cliffs or trees, in a similar manner to that employed by modern birds, and that powered flight eventually evolved from this usage. During its proposal, it was suggested that WAIR might have plausibly been used by feathered theropods like Caudipteryx to develop aerial flight.

Basal oviraptorosaurs
Caudipteridae
Caenagnathoidea

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