Nemegtosaurus

Reconstruction of the head of Nemegtosaurus

• Mongolia, Nemegt Uul

• Nemegtosaurus mongoliensis
• ? Nemegtosaurus pachi

Nemegtosaurus is a sauropod dinosaur from the group of Titanosauria, who lived in the Upper Cretaceous in what is now Mongolia. This genus is known from a nearly complete skull that was salvaged from the early Maastrichtian of Nemegt lineup and described as Nemegtosaurus mongoliensis ( Nowinski, 1971).

The phylogenetic relationships of Nemegtosaurus were long controversy. He was originally considered a Dicraeosaurus like sauropods and was classified within the Diplodocoidea - further studies postulated a position as sister taxon of Diplodocoidea. Recent studies believe in a position within the Titanosauria, which was confirmed in a redescription of the discovery by Wilson ( 2005).

The dinosaur fauna of the late Cretaceous Mongolia is known by numerous finds of theropod dinosaurs and birds Beck, which mainly come from the Barun - Goyot lineup and Djadochta lineup - to mention, for example, Protoceratops, Velociraptor and Tarbosaurus. Sauropods are rare in this fauna, as we know only two other finds from the Nemegt lineup: Quaesitosaurus and Opisthocoelicaudia. Quaesitosaurus is known by an incomplete skull and closely related to Nemegtosaurus while Opisthocoelicaudia based on a skull -less skeleton. These finds include along with the Nemegtosaurus Skull to the best preserved Sauropodenfossilien from the Late Cretaceous Laurasias ( the northern land masses ).

Fund and Research History

The type material ( holotype ) of Nemegtosaurus mongoliensis consists of a compressed, but nearly complete skull (including articulated mandible), the only parts of the upper face ( nose region ) are missing. Originally, the finding of a single block, but this was broken down into four parts after taxidermists the surrounding rock almost completely away.

There have been three attempts at reconstruction ( Nowinski, 1971, Salgado and Calvo, 1997, and Wilson, 2005), but contradict each other in certain characteristics. According to Wilson ( 2005) had the skull significant similarities with that of Rapetosaurus. The nasal openings were enlarged and there were diagonally across the tear-shaped orbital windows, the latter have ornaments on the top edge. The skull is elongated and its top falls off towards the front. The total of about 52 teeth are dünnkronig and pin-shaped, similar to the Diplodocoidea - show Nemegtosaurus and other Titanosaurier that dünnkronige teeth have developed in the evolution of sauropods at least twice independently. The pine show a continuous change of teeth: dentures expressed out to be replaced, worn teeth from below, at some positions seem replacement teeth to have emerged also in addition to the teeth to be replaced.

Dong (1977 ) described with Nemegtosaurus pachi another type based on teeth that have been discovered in the Turpan Basin in Xinjiang, China. However, this species is considered as a noun dubium and the assignment to Nemegtosaurus than doubtful. Wilson ( 2005) noted that the classification as the basis Nemegtosaurus missing since the supposed typical feature found in other titanosaurs for this genus. Maryanska (2000) mentioned another skull that could possibly belong to Nemegtosaurus, but has not yet been described.

Wilson ( 1997) suggested that the vestiges of Nemegtosaurus and might belong to the same species of Quaesitosaurus - but in his redescription (2005) he presented differences determined that justify separate genera. Because of Opisthocoelicaudia is no known skull material can not be excluded that this is identical to Nemegtosaurus what already Paul ( 1996) suspected.

System

Initially Nemegtosaurus and Quaesitosaurus were classified within the Dicraeosaurinae, due to similarities in skull structure and teeth. Upchurch (1995 ) placed Nemegtosaurus in the new family Nemegtosauridae, which should include all Diplodocoideen that were more closely related to Nemegtosaurus than Diplodocus. Rogers and Forster ( 2001) and Wilson ( 2002), however, came to the conclusion that Nemegtosaurus is to be settled within the Titanosauria - as defined Wilson ( 2005), the new Nemegtosauridae as a group of species that are more closely related than Nemegtosaurus with Saltasaurus. According to Wilson include at least the genera Nemegtosaurus, Quaesitosaurus and Rapetosaurus to this family.

The classification of the skulls of Nemegtosaurus and Quaesitosaurus was complicated by the general rarity of skull material in sauropods. Especially of titanosaurs is in large part only material of postcranial skeleton ( the " rest of the skeleton ," which follows behind the skull ) is known, there are only three skulls that have been described. The genus Rapetosaurus ( Curry Rogers and Forster, 2001) represents the single Fund, which shows almost complete skull material in connection with the rest of the skeleton.