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.

Nemegt Formation
Stratigraphic range: Maastrichtian
~70 Ma
TypeGeological formation
OverliesBarun Goyot Formation
Lithology
PrimaryShale, sandstone
Location
RegionGobi Desert
Country Mongolia

Description

The Nemegt Formation (the upper beds) are composed of shales and sandstones that were deposited by ancient lakes, streams, and flood plains. The Altan Ula locality was described by Michael Novacek (1996) as "a canyon carved out of a very rich series of sedimentary rocks" with "steep cliffs and narrow washes". The presence of petrified wood, and the remains of Araucariaceae conifers indicate that the forests of the Nemegt were thickly wooded, with a high canopy formed by tall conifer trees. When examined, the rock facies of this formation suggest the presence of stream and river channels, mudflats, and shallow lakes. Sediments also indicate that there existed a rich habitat, offering diverse food in abundant amounts that could sustain massive Cretaceous dinosaurs.[1]

Flora and fauna of the Nemegt Formation

Coelurosaurs

Oviraptorosaurs

Paravians

Other coelurosaurs

Invertebrates

Genus Species Location Stratigraphic Position Abundance Notes

Nemegtia

An ostracod.

Mammals

Genus Species Location Stratigraphic Position Abundance Notes Images

Buginbaatar

Buginbaatar transaltaiensis

A multituberculate.

"Gurlin Tsav skull"

A mysterious metatherian, possibly a sparassodont.

Ornithischians

Sauropods

Fossil Eggs

Oogenus Oospecies Location Stratigraphic Position Material Notes Images

Laevisoolithus[25]

Laevisoolithus sochavai

"Whole egg with partly broken pole"[25]

Laid by a bird or small theropod.[25]

Subtiliolithus[25]

Subtiliolithus microtuberculatus[25]

"Eggshell fragments"[25]

See also

References

  1. ^ Novacek, M. (1996). Dinosaurs of the Flaming Cliffs. Bantam Doubleday Dell Publishing Group Inc. New York, New York. ISBN 978-0-385-47775-8
  2. ^ Funston, G. F.; Mendonca, S. E.; Currie, P. J.; Barsbold, R. (2017). "Oviraptorosaur anatomy, diversity and ecology in the Nemegt Basin". Palaeogeography, Palaeoclimatology, Palaeoecology. doi:10.1016/j.palaeo.2017.10.023.
  3. ^ a b "Table 8.1," in Weishampel, et al. (2004). Page 167.
  4. ^ a b "Table 8.1," in Weishampel, et al. (2004). Page 166.
  5. ^ a b c d e f g h i j k l m Barsbold, R. (1983). "Carnivorous dinosaurs from the Cretaceous of Mongolia [in Russian]." Trudy, Sovmestnaâ Sovetsko−Mongol’skaâ paleontologičeskaâ èkspediciâ, 19: 1–120.
  6. ^ "Table 10.1," in Weishampel, et al. (2004). Page 198.
  7. ^ a b c "Table 9.1," in Weishampel, et al. (2004). Page 185.
  8. ^ Larry D. Martin, Evgeny N. Kurochkin and Tim T. Tokaryk (2012). "A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia". Palaeoworld. 21. doi:10.1016/j.palwor.2012.02.005.
  9. ^ "Table 11.1," in Weishampel, et al. (2004). Page 213.
  10. ^ "Table 11.1," in Weishampel, et al. (2004). Page 215.
  11. ^ Norell, M.A.; Makovicky, P.J.; Bever, G.S.; Balanoff, A.M.; Clark, J.M.; Barsbold, R.; Rowe, T. (2009). "A Review of the Mongolian Cretaceous Dinosaur Saurornithoides (Troodontidae: Theropoda)". American Museum Novitates. 3654: 63. doi:10.1206/648.1.
  12. ^ a b c "Table 6.1," in Weishampel, et al. (2004). Page 138.
  13. ^ "Table 5.1," in Weishampel, et al. (2004). Page 112.
  14. ^ http://www.dvidshub.net/image/1442492/gallimimus-slab#.U8V4urF5bAx
  15. ^ a b Michael G. Newbrey, Donald B. Brinkman, Dale A. Winkler, Elizabeth A. Freedman, Andrew G. Neuman, Denver W. Fowler and Holly N. Woodward (2013). "Teleost centrum and jaw elements from the Upper Cretaceous Nemegt Formation (Campanian-Maastrichtian) of Mongolia and a re-identification of the fish centrum found with the theropod Raptorex kreigsteini" (PDF). In Gloria Arratia; Hans-Peter Schultze; Mark V. H. Wilson. Mesozoic Fishes 5 – Global Diversity and Evolution. Verlag Dr. Friedrich Pfeil. pp. 291–303. ISBN 978-3-89937-159-8. Archived from the original (PDF) on 2015-09-24.CS1 maint: Multiple names: authors list (link)
  16. ^ Fowler DW, Woodward HN, Freedman EA, Larson PL, Horner JR (2011) Reanalysis of “Raptorex kriegsteini”: A Juvenile Tyrannosaurid Dinosaur from Mongolia. PLoS ONE 6(6): e21376. doi:10.1371/journal.pone.0021376
  17. ^ http://www.dvidshub.net/image/1442496/skull-tarbosaurus-baatar#.U8V7LrF5bAw
  18. ^ "Table 7.1," in Weishampel, et al. (2004). Page 152.
  19. ^ a b "Table 20.1," in Weishampel, et al. (2004). Page 441.
  20. ^ Arbour, V. M., Currie, P. J. and Badamgarav, D. (2014), The ankylosaurid dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia. Zoological Journal of the Linnean Society, 172: 631–652. doi: 10.1111/zoj.12185
  21. ^ "Table 21.1," in Weishampel, et al. (2004). Page 465.
  22. ^ Paul Penkalski; Tatiana Tumanova (2016). "The cranial morphology and taxonomic status of Tarchia (Dinosauria: Ankylosauridae) from the Upper Cretaceous of Mongolia". Cretaceous Research. in press. doi:10.1016/j.cretres.2016.10.004.
  23. ^ Philip J. Currie; Jeffrey A. Wilson; Federico Fanti; Buuvei Mainbayar; Khishigjav Tsogtbaatar, in press. Rediscovery of the type localities of the Late Cretaceous Mongolian sauropods Nemegtosaurus mongoliensis and Opisthocoelicaudia skarzynskii: Stratigraphic and taxonomic implications. Palaeogeography, Palaeoclimatology, Palaeoecology doi:10.1016/j.palaeo.2017.10.035.
  24. ^ "Table 13.1," in Weishampel, et al. (2004). Page 270.
  25. ^ a b c d e f K. E. Mikhailov. 1991. Classification of fossil eggshells of amniotic vertebrates. Acta Palaeontologica Polonica 36(2):193-238
Anserimimus

Anserimimus( AN-sər-i-MY-məs; "goose mimic") is a genus of ornithomimid theropod dinosaur, from the Late Cretaceous Period of what is now Mongolia. It was a lanky, fast-running animal, possibly an omnivore. From what fossils are known, it probably closely resembled other ornithomimids, except for its more powerful forelimbs.

Bagaraatan

Bagaraatan (/'ba-ɣa-raa-tan/ meaning 'small' baɣa + 'carnivorous animal, beast of prey' araatan in Mongolian) is a genus of theropod dinosaur from the Late Cretaceous period. Its fossils were found in the Nemegt Formation of Mongolia. Bagaraatan may have been around 3 to 4 metres (9.8 to 13 ft) in length.

The type species, B. ostromi, was described by Osmolska in 1996. The post-cranial (ZPAL MgD-I/108) skeleton has been described as "bird-like", while the skull exhibits features of several different theropod groups.

Barsboldia

Barsboldia (meaning "of Barsbold", a well-known Mongolian paleontologist) was a genus of large hadrosaurid dinosaur from the early Maastrichtian Nemegt Formation of Ömnogöv', Mongolia. It is known from a partial vertebral column, partial pelvis, and some ribs.

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.

Borogovia

Borogovia is a troodontid theropod dinosaur genus which lived during the Late Cretaceous Period, in what is now Mongolia.

In 1971, a Polish-Mongolian expedition discovered the remains of a small theropod at the Altan Ula IV site, in the Nemegt Basin of Ömnögovĭ province. In 1982, the find was reported by Halszka Osmólska and considered by her to be a possible specimen of Saurornithoides. Later she concluded that it represented a species new to science.

In 1987, Osmólska named and described the type species Borogovia gracilicrus. The generic name is derived from the fantasy creatures known as 'borogoves' in the Lewis Carroll poem "Jabberwocky", in his Alice's Adventures in Wonderland. The specific name is a combination of Latin gracilis, "lightly built", and crus, "shin", in reference to the elegant build of the lower leg.The holotype specimen, ZPAL MgD-I/174, was found in the Nemegt Formation, dating from the early Maastrichtian. It consists of two lower legs of a single individual, including fragments of both tibiotarsi, the undersides of both metatarsi and the second, third and fourth toes of each foot.The tibiotarsi have an estimated length of twenty-eight centimetres. Borogovia is about two meters (6 feet) long, weighing some twenty kilograms (forty-five pounds). The tibiotarsus is very elongated. The third toe is narrow. The second phalanx of the second toe is short. The claw of the second toe is short and relatively flat. Osmólska claimed that the second toe could not be hyperextended, and suggested that it had regained a weight-bearing function, compensating for the weakness of the third toe.Borogovia was assigned by Osmólska to the Troodontidae in 1987.

Conchoraptor

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

Deinocheirus

Deinocheirus ( DY-no-KY-rəs) is a genus of large ornithomimosaur that lived during the Late Cretaceous around 70 million years ago. In 1965, a pair of large arms, shoulder girdles, and a few other bones of a new dinosaur were first discovered in the Nemegt Formation of Mongolia. In 1970, this specimen became the holotype of the only species within the genus, Deinocheirus mirificus; the genus name is Greek for "horrible hand". No further remains were discovered for almost fifty years, and its nature remained a mystery. Two more complete specimens were described in 2014, which shed light on many aspects of the animal. Parts of these new specimens had been looted from Mongolia some years before, but were repatriated in 2014.

Deinocheirus was an unusual ornithomimosaur, the largest of the clade at 11 m (36 ft) long, and weighing 6.4 t (7.1 short tons). Though it was a bulky animal, it had many hollow bones which saved weight. The arms were among the largest of any bipedal dinosaur at 2.4 m (7.9 ft) long, with large, blunt claws on its three-fingered hands. The legs were relatively short, and bore blunt claws. Its vertebrae had tall neural spines that formed a "sail" along its back. The tail ended in pygostyle-like vertebrae, which indicate the presence of a fan of feathers. The skull was 1.024 m (3.36 ft) long, with a wide bill and a deep lower jaw, similar to those of hadrosaurs.

The classification of Deinocheirus was long uncertain, and it was initially placed in the theropod group Carnosauria, but similarities with ornithomimosaurians were soon noted. After more complete remains were found, Deinocheirus was shown to be a primitive ornithomimosaurian, most closely related to the smaller genera Garudimimus and Beishanlong, together forming the family Deinocheiridae. Members of this group were not adapted for speed, unlike other ornithomimosaurs. Deinocheirus is thought to have been omnivorous; its skull shape indicates a diet of plants, fish scales were found in association with one specimen and gastroliths were also present in the stomach region of the specimen. The large claws may have been used for digging and gathering plants. Bite marks on Deinocheirus bones have been attributed to the tyrannosaurid Tarbosaurus.

Gurilynia

Gurilynia is a genus of enantiornithine birds. One species is known, G. nessovi. It lived during the Maastrichtian stage of the Late Cretaceous period, between 70 and 66 mya. Gurilynia is known from fragmentary fossils found at the Gurilyn Tsav locality of the Nemegt Formation in south Gobi, Mongolia.

The fossil material includes three partial bones. The holotype is the proximal end of a right humerus, catalog number PIN 4499-12. A paratype is the distal end of a left humerus, catalog number PIN 4499-14. The last paratype is the shoulder end of a left coracoid, catalog number PIN 4499-13. All three fossils are in the collection of the Paleontological Institute of the Russian Academy of Sciences. The material is depicted in the journal with both photographs and illustrations. The humeral head is around 29mm wide. The largest enantiornithine from the Early Cretaceous is Pengornis, with a humeral head width of (17mm).Kurochkin also mentions that "The additional distal portions of the ulna, radius, and carpometacarpus from the same beds also very probably belong to the Enantiornithes." This passage may describe PIN 4499-1, which was later assigned to Teviornis. Kurochkin also adds that G. nessovi demonstrates that there were large Enantiornithids in Central Asia as well as the Americas at the end of the Cretaceous.

Gurlin Tsav skull

The "Gurlin Tsav" skull is a currently unnamed carnivorous metatherian fossil from the Nemegt Formation of Mongolia. Composed of a single semi-complete skull, this specimen is notable in regards to the evolution and systematics of Metatheria as a whole, and thus nigh-omnipresent in phylogenetic analyses of this group.

Judinornis

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

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

Laevisoolithus

Laevisoolithus is an oogenus of fossil egg. Its sole oospecies, L. sochavai, is native to the Nemegt Formation in Mongolia. Laevisoolithus is characterized by its thin, smooth eggshells. These eggs were probably laid by a bird or a small theropod.

Mononykus

Mononykus ( mə-NON-i-kəs, sometimes MON-oh-NY-kəs; meaning "one claw") was a theropod dinosaur from late Cretaceous Mongolia (Nemegt Formation, about 70 million years ago) with long, skinny legs. It moved about on two legs, was likely very nimble and could run at high speeds, something that would have been useful in the open flood plains where it lived. It had a small skull, and its teeth were small and pointed, suggesting that it ate insects and small animals, such as lizards and mammals. Its large eyes might have allowed Mononykus to hunt by night, when it was cooler and there would have been fewer predators about. Mononykus was originally named Mononychus in 1993, but later that year, it was renamed because the original name had already been used for a beetle named by Johann Schueppel, a German entomologist.

Nemegt Basin

The Nemegt Basin is a geographical area in the northwestern Gobi Desert, in Ömnögovi Province, southern Mongolia. It is known locally as the "Valley of the Dragons", since it is a source of many fossil finds, including dinosaurs, dinosaur eggs, and trace fossils.The main geological formations in the area are the Nemegt Formation, Barun Goyot Formation, and Djadochta Formation, in order of age, from youngest (most superficial) to oldest (deepest).

Opisthocoelicaudia

Opisthocoelicaudia is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is Opisthocoelicaudia skarzynskii. A well-preserved skeleton lacking only the head and neck was unearthed in 1965 by Polish and Mongolian scientists, making Opisthocoelicaudia one of the best known sauropods from the Late Cretaceous. Tooth marks on this skeleton indicate that large carnivorous dinosaurs had fed on the carcass and possibly had carried away the now-missing parts. To date, only two additional, much less complete specimens are known, including a part of a shoulder and a fragmentary tail. A relatively small sauropod, Opisthocoelicaudia measured about 11.4 metres (37 ft) in length. Like other sauropods, it would have been characterised by a small head sitting on a very long neck and a barrel shaped trunk carried by four column-like legs. The name Opisthocoelicaudia means "posterior cavity tail", alluding to the unusual, opisthocoel condition of the anterior tail vertebrae that were concave on their posterior sides. This and other skeletal features lead researchers to propose that Opisthocoelicaudia was able to rear on its hindlegs.

Named and described by Polish paleontologist Maria Magdalena Borsuk-Białynicka in 1977, Opisthocoelicaudia was first thought to be a new member of the Camarasauridae, but is currently considered a derived member of the Titanosauria. Its exact relationships within Titanosauria are contentious, but it may have been close to the North American Alamosaurus. All Opisthocoelicaudia fossils stem from the Nemegt Formation. Despite being rich in dinosaur fossils, the only other sauropod from this rock unit is Nemegtosaurus, which is known from a single skull. Since the skull of Opisthocoelicaudia remains unknown, several researchers have suggested that Nemegtosaurus and Opisthocoelicaudia may represent the same species. Sauropod footprints from the Nemegt Formation, which include skin impressions, can probably be referred to either Nemegtosaurus or Opisthocoelicaudia as these are the only known sauropods from this formation.

Presbyornithidae

Presbyornithidae is an extinct group of birds with a global distribution. They had evolved by the late Cretaceous period and became extinct during the early Miocene. Initially, they were believed to present a mix of characters shown by waterbirds, shorebirds and flamingos and were used to argue for an evolutionary relationship between these groups, but they are now generally accepted to be waterfowl closely related to modern ducks, geese, and screamers.They were generally long-legged, long-necked birds, standing around one meter high, with the body of a duck, feet similar to a wader but webbed, and a flat duck-like bill adapted for filter feeding. At least some species were social birds that lived in large flocks and nested in colonies, while others, like the Wilaru species, were terrestrial and solitary.Several genera have been classified as presbyornithids:

Presbyornis (type)

Headonornis (disputed)

Telmabates

Teviornis

Proherodius

Zhylgaia

WilaruThere are some other, undescribed, presbyornithid or possible presbyornithid remains, such as the partial right scapula BMNH PAL 4989, which was considered part of Headonornis hantoniensis, but cannot be positively refererred to a known taxon, or the Late Cretaceous remains from the Mongolian Barun Goyot Formation at Uday Sayr and the Nemegt Formation of Tsagaan Kushu.

Subtiliolithus

Subtiliolithus is an oogenus of fossil egg from Nemegt Formation of Mongolia. The eggs are notable for a very thin eggshell. It contains two oospecies: S. kachchhensis, and S. microtuberculatus. They were originally classified as a distinct oofamily, Subtiliolithidae, but numerous similarities to Laevisoolithus have led to their reclassification as Laevisoolithid eggs. A complete skeleton of Nanantius valifanovi was found associated with Subtiliolithus eggshells, indicating that the oogenus represents eggs of enantiornithine birds.

Tarbosaurus

Tarbosaurus ( TAR-bə-SAWR-əs; meaning "alarming lizard") is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China.

Although many species have been named, modern paleontologists recognize only one, T. bataar, as valid. Some experts see this species as an Asian representative of the North American genus Tyrannosaurus; this would make the genus Tarbosaurus redundant. Tarbosaurus and Tyrannosaurus, if not synonymous, are considered to be at least closely related genera. Alioramus, also from Mongolia, is thought by some authorities to be the closest relative of Tarbosaurus.

Like most known tyrannosaurids, Tarbosaurus was a large bipedal predator, weighing up to five tonnes and equipped with about sixty large teeth. It had a unique locking mechanism in its lower jaw and the smallest forelimbs relative to body size of all tyrannosaurids, renowned for their disproportionately tiny, two-fingered forelimbs.

Tarbosaurus lived in a humid floodplain criss-crossed by river channels. In this environment, it was an apex predator, probably preying on other large dinosaurs like the hadrosaur Saurolophus or the sauropod Nemegtosaurus. Tarbosaurus is represented by dozens of fossil specimens, including several complete skulls and skeletons. These remains have allowed scientific studies focusing on its phylogeny, skull mechanics, and brain structure.

Teviornis

Teviornis is a genus of extinct birds. One species has been described, T. gobiensis. It lived in the Maastrichtian stage at the end of the Late Cretaceous period, some 70 million years ago. It is known from fossils collected from the Nemegt Formation of Gobi, south Mongolia.

The fossils include only the holotype which are pieces of a crushed right forelimb. These pieces include a nearly complete right carpometacarpus, two phalanges, the radiale and ulnare of the wrist, and a fragment of the distal right humerus. The catalog number of these fossils are given multiple times as PIN 4499-1, but they are listed as PIN 44991-1 on page 3, where the holotype is formally listed. This is probably a misprint.The fossils were collected at the Gurilyn tsav locality, northwest corner of Umnogobi Aimak, Mongolia. They are in the collection

The genus name Teviornis is the Greek masculine word for bird combined with the name of Victor Tereschenko, the Paleontologist at the PIN who discovered the specimen. Gobiensis refers to the harsh Gobi Desert in which the fossil was found. The fossils are in the collection of the Paleontological Institute, Russian Academy of Sciences, Moscow.

Teviornis was described by Kurochkin, et al. as a member of the Presbyornithidae. These were stilt-legged, Anseriform, waterfowl which are extinct, but which flourished during the Late Cretaceous and Paleogene. If Teviornis does belong to the Presbyornithidae then, together with Vegavis from Antarctica, there is evidence that relatives of today's waterfowl already were widespread and highly apomorphic by the end of the Mesozoic.

A review of Kurochkin et al. was performed by Clarke and Norell in 2004. They concluded that some of the characters used by Kurochkin et al. to assign T. gobiensis to the Anseriformes, such as an unbowed metacarpal III, are plesiomorphies which are primitive for Avialae and also retained in some members of Ornithurae. They found that the remaining characters used by Kurochkin et al. also had wider distribution than was assumed, or had an incompletely studied distribution. Moreover, Clarke et al. found no synapomorphies of Aves (sensu Gauthier), Neognathae, or Galloanseres, preserved in PIN 4499-1. thus, they conclude, Teviornis cannot be assigned with any confidence to the Presbyornithidae.

Tochisaurus

Tochisaurus (meaning "Ostrich lizard") is a genus of small troodontid theropod dinosaur from the Late Cretaceous Period of Mongolia. The type (and only named) species is Tochisaurus nemegtensis.

In 1948, a Soviet-Mongolian expedition found the remains of a small theropod in the Gobi Desert near Nemegt. In 1987 the find was reported by Sergei Kurzanov and later that year discussed by Halszka Osmólska who suggested it could represent a specimen of the troodontid Borogovia.Later Osmólska understood it was a species new to science. It was formalized by Kurzanov and Osmólska in 1991 as Tochisaurus nemegtensis. The generic name is derived from Mongolian toch', "ostrich", in reference to the fact that the foot, like with that bird, is functionally didactyl, i.e. has only two weight-bearing toes. The specific name refers to the Nemegt.Its holotype fossil, PIN 551-224, was found in a layer of the Nemegt Formation, dating from the early Maastrichtian, about 69 million years old. It consists solely of the (left) metatarsus, the first discovered of an Asian troodontid. The first metatarsal is missing. The top of the fossil shows some damage that was originally somewhat inexpertly restored.Tochisaurus is a bipedal dinosaur. The metatarsus has a length of 242 millimetres, showing it was a relatively large troodontid. The second metatarsal, 222 millimetres long, is very reduced and narrow. The joint surface on top of the metatarsus is sloped forward and downward.Based on the partial fossils, Tochisaurus is thought to have been a member of the Troodontidae.

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