Avimimus

Avimimus (/ˌeɪvɪˈmaɪməs/ AY-vi-MY-məs), meaning "bird mimic" (Latin avis = bird + mimus = mimic), was a genus of oviraptorosaurian theropod dinosaur, named for its bird-like characteristics, that lived in the late Cretaceous in what is now Mongolia, around 70 million years ago.

Avimimus
Temporal range: Late Cretaceous, 70 Ma
Avimimus at TyrannosaursMeetTheFamily
Skeleton cast mount at Science Center of Iowa
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Oviraptorosauria
Superfamily: Caenagnathoidea
Family: Avimimidae
Kurzanov, 1981
Genus: Avimimus
Kurzanov, 1981
Type species
Avimimus portentosus
Kurzanov, 1981
Other species
  • Avimimus nemegtensis Funston et al., 2017

Description

Avimimus SIZE
Size of A. portentosus compared to a human

Avimimus was a small, bird-like dinosaur with a length of 1.5 m (5 ft).[1] The skull was small compared to the body, though the brain[1] and eyes were large. The size of the bones which surrounded the brain and were dedicated to protecting it are large.[1] This is also consistent with the hypothesis that Avimimus had a proportionally large brain.[1]

The jaws of Avimimus were thought to form a parrot-like beak lacking teeth, and a thorough review of the holotype specimen's anatomy confirmed that no teeth were preserved, although a series of tooth-like projections along the tip of the premaxilla were.[2] However, subsequently discovered specimens have been reported to preserve small premaxillary teeth.[3] The small teeth or possible lack thereof in Avimimus suggests that it may have been an herbivore or omnivore. Kurzanov himself, however, believed that Avimimus was an insectivore.[1]

The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in Avimimus.[1] The occipital condyle, however, was small, further suggestive of the skull's relative lightness.[1] The neck itself was long and slender, and is composed of vertebrae that are much more elongate than in other oviraptorosaurs. Unlike oviraptorids and caenagnathids, the back vertebrae lack openings for air sacs, suggesting that Avimimus is more primitive than these animals.

Avimimus mmartyniuk wiki
Restoration of A. portentosus

The forelimbs were relatively short. The bones of the hand were fused together, as in modern birds, and a ridge on the ulna (lower arm bone) was interpreted as an attachment point for feathers by Kurzanov.[1][4] Kurzanov, in 1987, also reported the presence of quill knobs,[1][5] and while Chiappe confirmed the presence of bumps on the ulna, their function remained unclear.[2] Kurzanov was so convinced they were attachment points for feathers that he concluded that Avimimus may have been capable of weak flight.[1] The presence of feathers is now widely accepted, but most paleontologists do not believe Avimimus could fly.[1]

The ilium was almost horizontally oriented, resulting in exceptionally broad hips. Little is known of the tail but the hip suggests that the tail was long. The legs were extremely long and slender, suggesting that Avimimus was a highly specialized runner. The proportions of the leg bones add further weight to the idea of Avimimus was quick on its feet.[1] The animal's shins were long in comparison with its thighs,[1] a trait common among cursorial animals. It also had three-toed feet with narrow pointed claws.

Discovery and species

Avimimus portentosus
Skeletal diagram showing some known elements of A. portentosus

The remains of Avimimus were recovered by Russian paleontologists[1] and officially described by Dr. Sergei Kurzanov in 1981. The Avimimus fossils were initially described as having come from the Djadokta Formation by Kurzanov; however, in a 2006 description of a new specimen, Watabe and colleagues noted that Kurzanov was probably mistaken about the provenance, and it is more likely that Avimimus hailed from the more recent Nemegt Formation.[6] The type species is A. portentosus.[4] Because no tail was found with the original find, Kurzanov mistakenly concluded that Avimimus lacked a tail in life.[1] However, subsequent Avimimus finds containing caudal vertebrae have confirmed the presence of a tail.[1] A second nearly complete specimen of Avimimus was discovered in 1996 and described in 2000 by Watabe and colleagues. Additionally, these authors identified a number of small theropod footprints in the same area as belonging to Avimimus.[3]

Avimimus excavation
Excavation at a bonebed of A. nemegtensis reported in 2006

A variety of isolated bones that have been attributed to Avimimus were considered to be distinct from A. portentosus, and were initially referred to as Avimimus sp.[7] In 2008, a team of Canadian, American, and Mongolian paleontologists headed by Phil Currie reported the 2006 an extensive bonebed of Avimimus sp. fossils, discovered in 2006. The bonebed is in the Nemegt Formation, 10.5 meters above the Barun Goyot Formation, in the Gobi Desert. The team reported finding abundant bones of at least ten individuals of Avimimus, but the deposit may hold more. All individuals were either adult or subadult, and the adults showed little variation in size, suggesting determinate growth. The team also suggests that the individuals were found together because they were gregarious in life, providing possible indications that Avimimus formed age-segregated groups for either lekking or flocking purposes. The adults showed a greater degree of skeletal fusion in the tarsometatarsus and tibiotarsus, and also more prominent muscle scars. The preservation of the bonebeds suggest that they were buried rapidly, uncovered by rapid flow of water, and then buried again a short distance away.[8][9] In 2018, Avimimus sp. was formally described as a new species, A. nemegtensis.[10]

Classification

Avimimus was originally suggested to be a very close relative of birds, given its unique suite of bird-like features not known in other dinosaurs at the time. In fact, Kurzanov argued that Avimimus, rather than the famous early bird Archaeopteryx, was close to the direct ancestor of modern birds, and that Archaeopteryx was not as closely related to birds as had previously been suggested.[5] However, this view has not been supported by later phylogenetic analyses of dinosaur and bird relationships. Most modern scientists find that Avimimus in fact belongs to a diverse group of bird-like dinosaurs more primitive than Archaeopteryx, the oviraptorosaurs.[11][12]

Avimimus dentaries
Partial dentary bones of A. nemegtensis

Kurzanov placed Avimimus in its own family, Avimimidae, in 1981. In 1991, Sankar Chatterjee erected the Order Avimimiformes to include Avimimus. Neither of these group names is used frequently by paleontologists as they include only a single species. More recent studies have shown that Avimimus is best grouped within the Oviraptoridae, within the subgroup Elmisaurinae.[13]

The following cladogram follows an analysis by Phil Senter, 2007.[14]

Caenagnathoidea

Avimimus

Caenagnathus

unnamed

Caudipteryx

Microvenator

Oviraptoridae

Oviraptor

unnamed

IGM 100/42

Rinchenia

unnamed

Citipati

unnamed

Chirostenotes

Elmisaurus

Hagryphus

Ingeniinae
unnamed

Ingenia

Heyuannia

unnamed

Conchoraptor

Khaan

Paleoecology

Avimimus nasal bones
Nasal bones of A. nemegtensis

The Barun Goyot Formation of Mongolia, is estimated to date back to the Campanian stage, between 84 and 70 million years ago[15] of the Late Cretaceous period.[16] During the Late Cretaceous period, the land that is now the Barun Goyot Formation had an arid environment with fields of sand dunes and only intermittent streams. It is slightly younger than the nearby Djadochta Formation, and seems to have been slightly wetter.[16] This formation is noteworthy for the exquisite preservation of small and fragile dinosaur skeletons, a rare occurrence considering that these fossils are typically broken up and dispersed when found in other rock formations.[17]

Avimimus skull new
Skull diagram of A. nemegtensis

The region that is preserved in the Barun Goyot Formation was home to the maniraptoran Hulsanpes perlei, the oviraptorids Conchoraptor gracilis and Ajancingenia yanshini, the alvarezsaurids Ceratonykus oculatus, Mononykus and Parvicursor remotus, the pachycephalosaur Tylocephale gilmorei, the ankylosaurs Saichania chulsanensis and Tarchia gigantea, and the ceratopsians Bagaceratops rozhdestvenskyi, Breviceratops kozlowskii, Lamaceratops tereschenkoi and Platyceratops tatarinovi. The largest dinosaur among them was the titanosaur Quaesitosaurus orientalis. It was observed that many of the same genera were present at the Barun Goyot and Djadochta Formations, though there was variation at the species level.[18] Vertebrates present in the Barun Goyot Formation included the primitive birds Gobipteryx minuta and Hollanda luceria and the lizards Estesia mongoliensis, Ovoo gurvel, Proplatynotia longirostrata and Gobiderma pulchrum. The early mammals that were present in this region during the time of Avimimus were the placental mammals Asioryctes nemegetensis and Barunlestes butleri, the amphibian Gobiates khermeentsavi, the multituberculate mammals Catopsbaatar catopsaloides, Chulsanbaatar vulgaris and Nemegtbaatar gobiensis, and the marsupial mammal Asiatherium reshetovi and Deltatheridium pretrituberculare. Numerous dinosaur eggshells found in this region support the presence of sauropods and maniraptors.

See also

References

  1. ^ a b c d e f g h i j k l m n o p "Avimimus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 130. ISBN 0-7853-0443-6.
  2. ^ a b Chiappe, L.M. and Witmer, L.M. (2002). Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press, 536 pp. ISBN 0-520-20094-2
  3. ^ a b Watabe, Weishampel; Barsbold, Tsogtbaatar; Suzuke (2000). "New nearly complete skeleton of the bird-like theropod, Avimimus, from the Upper Cretaceous of the Gobi Desert, Mongolia". Journal of Vertebrate Paleontology. 20 (3): 77A.
  4. ^ a b Kurzanov, S.M. (1981). "An unusual theropod from the Upper Cretaceous of Mongolia Iskopayemyye pozvonochnyye Mongolii (Fossil Vertebrates of Mongolia)." Trudy Sovmestnay Sovetsko-Mongolskay Paleontologiyeskay Ekspeditsiy (Joint Soviet-Mongolian Paleontological Expedition), 15: 39-49. Nauka Moscow, 1981
  5. ^ a b Kurzanov, S.M. (1987). "Avimimidae and the problem of the origin of birds." Transactions of the Joint Soviet-Mongolian Paleontological Expedition, 31: 5-92. [in Russian]
  6. ^ Watabe; Suzuki; Tsogtbaatar (2006). "Geological and geographical distribution of bird-like theropod, Avimimus in Mongolia". Journal of Vertebrate Paleontology. 26 (3): 136A–137A. doi:10.1080/02724634.2006.10010069.
  7. ^ Ryan, Currie; Russell, D. (2001). "New material of Avimimus portentosus (Theropoda) from the Iren Debasu Formation (Upper Cretaceous) of the Erenhot Region of Inner Mongolia". Journal of Vertebrate Paleontology. 21 (3): 95A. doi:10.1080/02724634.2001.10010852.
  8. ^ Currie, P.; Longrich, N.; Ryan, M.; Eberth, D.; Demchig, B. (2008). "A bonebed of Avimimus sp. (Dinosauria: Theropoda) from the Late Cretaceous Nemegt Formation, Gobi Desert: Insights into social behavior and development in a maniraptoran theropod". Journal of Vertebrate Paleontology. 28 (3): 67A. doi:10.1080/02724634.2008.10010459.
  9. ^ Funston, G.F.; Currie, P.J.; Eberth, D.A.; Ryan, M.J.; Chinzorig, T.; Badamgarav, D.; Longrich, N.R. (2016). "The first oviraptorosaur (Dinosauria: Theropoda) bonebed: evidence of gregarious behaviour in a maniraptoran theropod". Scientific Reports. 6: 35782. doi:10.1038/srep35782. PMC 5073311. PMID 27767062.
  10. ^ Funston, G.F.; Mendonca, S.E.; Currie, P.J.; Barsbold, R. (2018). "Oviraptorosaur anatomy, diversity and ecology in the Nemegt Basin". Palaeogeography, Palaeoclimatology, Palaeoecology. in press. doi:10.1016/j.palaeo.2017.10.023.
  11. ^ Dyke; Thorley (1998). "Reduced cladistic consensus methods and the avian affinities of Protoavis and Avimimus". Archaeopteryx. 16: 123–129.
  12. ^ 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. doi:10.1126/science.1144066. PMID 17823350.
  13. ^ Holtz, Thomas R. Jr. (2010) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2010 Appendix.
  14. ^ Senter, P. (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology, (doi:10.1017/S1477201907002143).
  15. ^ Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2005). A Geologic Time Scale 2004. Cambridge: Cambridge University Press. ISBN 978-0-521-78142-8.
  16. ^ a b Jerzykiewicz, Tomasz; Russell, Dale A. (1991). "Late Mesozoic stratigraphy and vertebrates of the Gobi Basin". Cretaceous Research. 12 (4): 345–377. doi:10.1016/0195-6671(91)90015-5.
  17. ^ Novacek, M. J., 1996. "Dinosaurs of the Flaming. Cliffs" Anchor/Doubleday. 367 p.
  18. ^ Nicholas R. Longrich; Philip J. Currie; Dong Zhi-Ming (2010). "A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia". Palaeontology. 53 (5): 945–960. doi:10.1111/j.1475-4983.2010.00968.x.
1981 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 1981.

Barun Goyot Formation

The Barun Goyot Formation (West Goyot Formation) is a geological formation dating to the Late Cretaceous Period. It is located within and is widely represented in the Gobi Desert Basin, in the Ömnögovi Province of Mongolia.

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.

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.

Two species have been described; C. zoui (the type species), in 1998, and C. dongi, in 2000.Caudipteryx fossils were first discovered in the Yixian Formation of the Sihetun area of Liaoning Province, northeastern China in 1997.

Conchoraptor

Conchoraptor (meaning "conch plunderer") is a genus of oviraptorid dinosaur from the late Cretaceous Period of what is now Asia.

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.

Iren Dabasu Formation

The Iren Dabasu Formation is a Mesozoic geologic formation in the Iren Nor region of Inner Mongolia. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.

It is located in the Iren Nor region of China, and dates from the Upper Cretaceous.

It is typically referred to continental clastic sediments consisting of light grey fine sandstones, coarse sandstones and glutenites as well as mottled claystones and siltstones. This lithological unit has yielded plentiful dinosaur remains in quantity and group, also including a great deal of microfossil material. The stratigraphic sequence, sedimentary system, and the morphologies and assemblages of the paleontological taxa are summarized on the basis of previous studies on the Iren Dabasu Formation. The fine-grained floodplain sediments and the coarse-grained sediments of the point bar formed a series of repeated frequently binary sedimentary rhythms. The “binary structure” of the sedimentary rhythms strongly indicates meandering stream deposits rather than braided river deposits as previously thought. The ostracod and charophyte assemblages of the Iren Dabasu Formation has suggested a potential correlation with those of the Sifangtai Formation and the basal Mingshui Formation in the Songliao Basin (mid/late Campanian age). Vertebrates point to an older date than middle-late Campanian. The turtle Khunnuchelys is known from both Iren Dabasu and Baynshirenian-equivalent units such as the Bostobe and Bissekty. In addition, a giant Caenagnathid similar to Gigantoraptor is now known from the Baynshirenian beds of Tsagaan Teg. Like the coeval Baynshiree (or possibly Javkhlant) Formation in the Gobi, the dinosaur fauna of the Iren Dabasu Formation includes tyrannosaurs, ornithomimids, therizinosaurs and oviraptors. Gigantism, such in the case of Gigantoraptor, may have been due the humid climate of the Iren Nor region during the Late Cretaceous. It may also have been due to weak contemporary tyrannosaurs, as predator decline tends to maximize herbivore diversity.

John Payne (voice actor)

John Payne is an English actor and voice actor who was originally in the UK and now works with Ocean Studios in Vancouver, British Columbia. He has played several roles in anime, most notably Ramba Ral in Mobile Suit Gundam and Rasetsu in Inuyasha.

List of Asian dinosaurs

This is a list of dinosaurs whose remains have been recovered from Asia excluding the Indian Subcontinent, which was part of a separate landmass for much of the Mesozoic. This list does not include dinosaurs that live or lived after the Mesozoic age such as birds.

List of dinosaur genera

This list of dinosaurs is a comprehensive listing of all genera that have ever been included in the superorder Dinosauria, excluding class Aves (birds, both living and those known only from fossils) and purely vernacular terms.

The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomen dubium), or were not formally published (nomen nudum), as well as junior synonyms of more established names, and genera that are no longer considered dinosaurs. Many listed names have been reclassified as everything from birds to crocodilians to petrified wood. The list contains 1559 names, of which approximately 1192 are considered either valid dinosaur genera or nomina dubia.

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.

Nankangia

Nankangia is an extinct genus of caenagnathoid oviraptorosaurian dinosaur known from the Late Cretaceous Nanxiong Formation of Nankang County, Ganzhou City of Jiangxi Province, southeastern China. It contains a single species, Nankangia jiangxiensis. N. jiangxiensis coexisted with at least four other caenagnathoids, including an unnamed oviraptorid, Banji long, Ganzhousaurus nankangensis and Jiangxisaurus ganzhouensis. The relatively short dentary and non-downturned mandibular symphysis of Nankangia suggest that it may have been more herbivorous than carnivorous.

Nemegt Formation

The Nemegt Formation (or Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. It overlies and sometimes interfingers with the Barun Goyot Formation. Interfingering has been noted at the stratotype (Red Walls) and Khermeen Tsav. It consists of river channel sediments and contains fossils of fish, turtles, crocodilians, and a diverse fauna of dinosaurs, including birds. The climate associated with it was wetter than when preceding formations were deposited; there seems to have existed at least some degree of forest cover. Fossilized trunks have been also found.

There has been no absolute dating of the Nemegt Formation. It is, however, almost certainly early Maastrichtian c 71-70 Ma. Gradzinski and others considered a Campanian age possible but more recent research indicates otherwise. A Campanian age no longer seems credible, because the Alagteegian (or lower Djadokhtan, at the locality "Chuluut Uul") has been radiometrically dated at about 73.5 Ma or even younger (a more recent K/Ar date is 71.6 +/- 1.6 Ma). The c 73.5 (or perhaps 72) Ma Alagteegian is separated from the Nemegt by the "classic" Djadokhtan (e.g. Bayan Dzag), later Djadohktan (represented by Ukhaa Tolgod) and Barungoyotian (Khulsan). All these intervening horizons almost certainly represent more than the 1.5 million years between the dated Alagteegian level and the onset of Maastrichtian time (72.1 million Ma according to current dating). Ergo the Nemegt is entirely Maastrichtian. See also Shuvalov, Sochava and Martinsson The Age of Dinosaurs in Russia and Mongolia. The presence of Saurolophus further supports an early Maastrichtian age as the same genus occurs in the early Maastrichtian Horseshoe Canyon formation.

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).

Postorbital bar

The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket . It is a trait that only occurs in mammalian taxa, such as most strepsirrhine primates and the hyrax, while haplorhine primates have evolved fully enclosed sockets. One theory for this evolutionary difference is the relative importance of vision to both orders. As haplorrhines (tarsiers and simians) tend to be diurnal, and rely heavily on visual input, many strepsirrhines are nocturnal and have a decreased reliance on visual input.Postorbital bars evolved several times independently during mammalian evolution and the evolutionary histories of several other clades. Some species, such as Tarsiers, have a postorbital septum. This septum can be considered as joined processes with a small articulation between the frontal bone, the zygomatic bone and the alisphenoid bone and is therefore different to the postorbital bar, while it forms a composite structure together with the postorbital bar. Other species such as dermopterans have postorbital processes, which is a more primitive incomplete stage of the postorbital bar.

Sapeornis

Sapeornis is a type of avialan which lived during the early Cretaceous period (late Aptian to early Albian, roughly 125-120 mya). The genus Sapeornis contains only one species, Sapeornis chaoyangensis.

Sergei Kurzanov

Sergei Mikhailovich Kurzanov (Сергей Михайлович Курзанов, born 1947) is a Russian (formerly Soviet) paleontologist at the Paleontological Institute of the Russian Academy of Sciences. He is known mainly for his work in Mongolia and the ex-Soviet republics in Central Asia. In 1976 he announced the discovery of Alioramus. In 1981 he announced the discovery of Avimimus.In 1998 a species of iguanodont dinosaur from Mongolia was named Altirhinus kurzanovi in his honor.

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.

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