| Nemegtosaurus | |
|---|---|
 | |
| Cast of the skull ofNemegtosaurus on a reconstructedOpisthocoelicaudia skeleton,Museum of Evolution of Polish Academy of Sciences,Warsaw | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Titanosauria |
| Family: | †Nemegtosauridae |
| Genus: | †Nemegtosaurus Nowinski, 1971 |
| Species: | †N. mongoliensis |
| Binomial name | |
| †Nemegtosaurus mongoliensis Nowinski, 1971 | |
Nemegtosaurus (meaning "reptile from the Nemegt") was asauropoddinosaur from the LateCretaceousPeriod of what is nowMongolia. Measuring an estimated 12–13 m (39–43 ft) long and weighing 20 t (44,000 lb), it was named after theNemegt Basin in theGobi Desert, where the remains — a singleskull — were found. The skull resembles diplodocoids in being long and low, with pencil-shaped teeth. However, recent work has shown thatNemegtosaurus is in fact atitanosaur, closely related to animals such asSaltasaurus,Alamosaurus, andRapetosaurus.
The skull ofNemegtosaurus comes from the same beds as the titanosaurOpisthocoelicaudia, which is known from a skeleton lacking the neck and skull. Originally, the referral ofNemegtosaurus to Diplodocoidea andOpisthocoelicaudia 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.[1] Relocation of theNemegtosaurus type locality in Central Sayr and discovery of postcrania comparable to thoseOpisthocoelicauda holotype at theNemegtosaurus holotype locality has discussed the possibility thatOpisthocoelicauda is a junior synonym. Consequently, Opisthocoelicaudiinae would be a junior synonym of Nemegtosauridae.[2] In 2019, Alexander O. Averianov and Alexey V. Lopatin in a paper describing new specimens ofNemegtosaurus 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 toNemegtosaurus.[3]
Thetype species,Nemegtosaurus mongoliensis, was first described by Nowinski in 1971 on the basis ofZPAL MgD-I/9.[4] A second species,N. pachi, was described by Dong in 1977 on the basis of the teethIVPP V.4879, recovered from theSubashi Formation, but this non-diagnostic species is considered anomen dubium and cannot be referred to Nemegtosauridae.[5][6]
The cladogram below follows Franca et al. (2016):[7]
| Lithostrotia |
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One of two sauropods discovered in theNemegt formation alongsideOpisthocoelicaudia,Nemegtosaurus was a fairly sized sauropod dinosaur, estimated to measure between 12 and 13 m (39 and 43 ft) and weigh around 20 t (44,000 lb). 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 ofNemegtosaurus 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 whetherNemegtosaurus browsed high in the trees or grazed on low-growing plants; related titanosaurs include both long-necked browsing forms likeRapetosaurus and short-necked forms likeBonitasaura.
Comparisons between thescleral rings ofNemegtosaurus and modern birds and reptiles suggest that it may have beencathemeral, active throughout the day at short intervals.[8]
Nemegtosaurus is found in the Maastrichtian aged (66-72 Ma)Nemegt Formation, 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 ornithomimidGallimimus, the alvarezsauridMononykus, the velociraptorineAdasaurus, and the giant, saber-clawed therizinosaurTherizinosaurus. It also lived alongside the tyrannosaurTarbosaurus. With its possible body length of 12 metres (39 ft),[9] an adultNemegtosaurus may have been able to defend againstTarbosaurus, but juveniles would have been vulnerable.
