Nemegtosaurus
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''Nemegtosaurus'' (meaning 'Reptile from the Nemegt') was a
sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
from the Late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...
of what is now
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
. It was named after the
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, ...
in the
Gobi Desert The Gobi Desert (Chinese: 戈壁 (沙漠), Mongolian: Говь (ᠭᠣᠪᠢ)) () is a large desert or brushland region in East Asia, and is the sixth largest desert in the world. Geography The Gobi measures from southwest to northeast an ...
, where the remains — a single
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
— were found. The skull resembles diplodocoids in being long and low, with pencil-shaped teeth. However, recent work has shown that ''Nemegtosaurus'' is in fact a
titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...
, closely related to animals such as ''
Saltasaurus ''Saltasaurus'' (which means "lizard from Salta") is a genus of saltasaurid dinosaur of the Late Cretaceous period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, ''Saltasaurus'' was characterized by ...
'', ''
Alamosaurus ''Alamosaurus'' (; meaning "Ojo Alamo lizard") is a genus of opisthocoelicaudiine titanosaurian sauropod dinosaurs, containing a single known species, ''Alamosaurus sanjuanensis'', from the late Cretaceous Period of what is now southern North Am ...
'' and ''
Rapetosaurus ''Rapetosaurus'' ( ) is a genus of titanosaurian sauropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period. Only one species, ''Rapetosaurus krausei'', has been identified. Like other sauropod ...
''.


Discovery and taxonomy

The skull of ''Nemegtosaurus'' comes from the same beds as the titanosaur ''
Opisthocoelicaudia ''Opisthocoelicaudia'' is a genus of sauropod dinosaur of the late Cretaceous, Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is ''Opisthocoelicaudia skarzynskii''. A well-preserved skeleton lacking only the ...
'', which is known from a skeleton lacking the neck and skull. Originally, the referral of ''Nemegtosaurus'' to Diplodocoidea and ''Opisthocoelicaudia'' to Camarasauridae argued that the two represented different species. Both of these genera represent advanced titanosaurians, however, raising the possibility that the two are in fact the same animal. Relocation of the ''Nemegtosaurus'' type locality in Central Sayr and discovery of postcrania comparable to those ''Opisthocoelicauda'' holotype at the ''Nemegtosaurus'' holotype locality has discussed the possibility that ''Opisthocoelicauda'' is a junior synonym. Consequently, Opisthocoelicaudiinae would be a junior synonym of Nemegtosauridae. In 2019, Alexander O. Averianov and Alexey V. Lopatin in a paper describing new specimens of ''Nemegtosaurus'' reanalyzed the argument for synonymy and determined that the taxa were not synonymous because shared characters between the species were either difficult to determine or based on comparisons with a specimen which actually belonged to ''Nemegtosaurus.'' The
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
, ''Nemegtosaurus mongoliensis'', was first described by Nowinski in 1971 on the basis of ZPAL MgD-I/9. A second species, ''N. pachi'', was described by Dong in 1977 on the basis of the teeth IVPP V.4879, but is a ''
nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...
''.


Classification

The cladogram below follows Franca ''et al.'' (2016):


Description

Like other titanosaurs, the teeth are slender pencil-like structures that are ground down at a sharp angle to produce a chisel-like tip. The diet of ''Nemegtosaurus'' is unknown, however. There are no plant fossils from the Gobi, but during the Late Cretaceous, flowering plants became increasingly diverse, although in many environments ferns and conifers were still more common. Neither is it clear whether ''Nemegtosaurus'' browsed high in the trees or grazed on low-growing plants; related titanosaurs include both long-necked browsing forms like ''Rapetosaurus'' and short-necked forms like '' Bonitasaura''. Comparisons between the scleral rings of ''Nemegtosaurus'' and modern birds and reptiles suggest that it may have been
cathemeral Cathemerality, sometimes called metaturnality, is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood ar ...
, active throughout the day at short intervals.


Paleoenvironment

''Nemegtosaurus'' is found in the Maastrichtian aged (66-72 Ma)
Nemegt Formation The Nemegt Formation (also known as Nemegtskaya Svita) is a geological formation in the Gobi Desert of Mongolia, dating to the Late Cretaceous. The formation consists of river channel sediments and contains fossils of fish, turtles, crocodilian ...
, which makes it one of the last sauropods on earth. There, on a lush river delta flowing through the ancient sands of the Gobi Desert, ''Nemegtosaurus'' would have coexisted with animals like the ornithomimid ''
Gallimimus ''Gallimimus'' ( ) is a genus of theropod dinosaur that lived in what is now Mongolia during the Late Cretaceous period, about seventy million years ago (mya). Several fossils in various stages of growth were discovered by Polish-Mongolian exped ...
'', the alvarezsaurid ''
Mononykus ''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of alvarezsaurid dinosaur that lived during the Late Cretaceous in what is now Asia on the Nemegt Formation, about 70 million years ago. ''Mononykus'' was a very small theropod, estim ...
'', the velociraptorine ''
Adasaurus ''Adasaurus'' ( ; meaning "Ada lizard") is a genus of dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous period about 70 million years ago. The genus is known from two partial specimens found in the Nemegt Formation of Mongolia ...
'', and the giant, saber-clawed therizinosaur ''
Therizinosaurus ''Therizinosaurus'' (; meaning 'scythe lizard') is a genus of very large therizinosaurid that lived in Asia during the Late Cretaceous period in what is now the Nemegt Formation around 70 million years ago. It contains a single species, ''Theriz ...
''. It also lived alongside the tyrannosaur ''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus ba ...
''. Its size (estimated at 40 feet long) may have offered an adult some protection against ''
Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of tyrannosaurid dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period, considered to contain a single known species, ''Tarbosaurus ba ...
,'' but juveniles would have been vulnerable.


References

* Nowinski, A. (1971). ''Nemegtosaurus mongoliensis'' n. gen., n. sp. (Sauropoda) from the uppermost Cretaceous of Mongolia. ''Palaeontologia Polonica'' 25: 57–81. * Wilson, J. (2005). Redescription of the Mongolian sauropod ''Nemegtosaurus mongoliensis'' Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. ''Journal of Systematic Palaeontology.'' 3. 283 - 318. 10.1017/S1477201905001628. {{Portal bar, Dinosaurs, Cretaceous Nemegt fauna Late Cretaceous dinosaurs of Asia Lithostrotians Fossil taxa described in 1971 Fossils of Mongolia