Nemegtosaurus

Nemegtosaurus, the Nemegt lizard, was a sauropod dinosaur from Late Cretaceous Period of Mongolia. Nemegtosaurus was named after the Nemegt Basin in theGobi 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 Dreadnoughtus. 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 may have offered an adult some protection against Tarbosaurus, but juveniles would have been vulnerable. 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).

Relationship with Opisthocoelicaudia
Nemegtosaurus is one of two sauropods known from the Nemegt Basin, the other being the related Opisthocoelicaudia. Initially, both were wrongly classified as a diplodocoid and a camarasaurid, respectively, so they were thought to be unrelated. However, now that it is known they both represent advanced, closely related titanosaurs, it is thought that Nemegtosaurus and Opisthocoelicaudia may be one and the same. In that case, the name Nemegtosaurus would have priority, as it was classified first.