Nemegtosaurus

*Nemegtosaurus mongoliensis*

***Nemegtosaurus*** (meaning 'Nemegt lizard') was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. *Nemegtosaurus* was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — 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, closely related to animals such as *Saltasaurus*, *Alamosaurus*, and *Rapetosaurus*.

## Discovery and taxonomy

The skull of *Nemegtosaurus* comes from the same beds as the titanosaur *Opisthocoelicaudia*, 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. The recognition that both represent advanced titanosaurians, however, raises the possibility that the two are in fact the same animal. The Nemegt Formation has been well-explored, with dozens of skeletons collected over the course of many decades, but there is nothing to suggest more than one species of sauropod in the formation, which supports the idea that *Nemegtosaurus* and *Opisthocoelicaudia* in fact are the head and body of the same animal, but skeletons preserving the head and skull have not been found yet.The type species, *Nemegtosaurus mongoliensis*, was first described by Nowinski in 1971. A second species, *N. pachi*, was described by Dong in 1977, but is a nomen dubium.

## 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, active throughout the day at short intervals.

## Paleoenvironment

*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 ornithomimid *Gallimimus*, the alvarezsaurid Mononykus, the velociraptorine *Adasaurus*, and the giant, saber-clawed therizinosaur *Therizinosaurus*. It also lived alongside the tyrannosaur *Tarbosaurus*. Its size (estimated at 40 feet long) may have offered an adult some protection against *Tarbosaurus,* but juveniles would have been vulnerable.

## JPInstitute.com Description

Nemegtosaurus was a medium-sized, long-necked plant-eater from China. This dinosaur was a member of the same family of sauropods as Diplodocus. Before Nemegtosaurus was discovered, it was thought that this whole family had died out near the end of the Jurassic Period. This dinosaur lived almost 80 million years after that.

Nemegtosaurus' relationship to diplodocids has caused quite a bit of discussion among sauropod specialists. Its features appear to be those of a diplodocid, but its existence during the Late Cretaceous doesn't fit very neatly into the view of sauropod evolution.

## Links

http://web.archive.org/web/20030813092219/http://www.jpinstitute.com/dinopedia/dinocards/dc\_nemeg.html