Nemegtosauridae

Nemegtosauridae is a family of titanosaurian sauropod dinosaurs based originally on two late Cretaceous Mongolian species known only from their diplodocid-like skulls: Nemegtosaurus and Quaesitosaurus.

History of classification
Due to the diplodocid-like nature of the taxa placed in Nemegtosauridae, the systematic position of this family in Sauropoda was disputed until recently. McIntosh (1990) included both these animals in the family Diplodocidae, subfamily Dicraeosaurinae, as they resemble the skull of Dicraeosaurus, although differing in certain details.  Although the skull of Nemegtosaurus was found in the same formation as the headless skeleton of Opisthocoelicaudia, McIntosh (1990) kept Nemegtosaurus in Diplodocoidea while keeping Opisthocoelicauda separate from the former, a position reiterated by Upchurch (1995, 1999), and Upchurch et al. (2004). A cladistic analysis published in 2002 transferred Nemegtosaurus and Opisthocoelicauda from Diplodocoidea to Titanosauria.

Apesteguia (2004), in a paper describing a new Patagonian sauropod, Bonitasaura salgadoi, may have been the first to properly define the taxon, although without the use of cladistic analysis: the stemclade consisting of all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus.  He argued for a close relationship between Nemegtosaurus, Quaesitosaurus, Rapetosaurus, and Bonitasaura and referred to the previous phylogenetic analysis and use of Nemegtosauridae by Wilson (2002).

In his redescription of the Nemegtosaurus holotype, Wilson (2005) elaborated on the titanosaurian nature of Nemegtosaurus, defining Nemegtosauridae as a stem-based clade that includes all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus.  He also suggested that Opisthocoelicaudia may eventually be shown to be a junior synonym of Nemegtosaurus. For her part, Kristina Curry Rogers (see also Cuury Rogers and Forster [2001]) agreed with Wilson that both Nemegtosaurus and Quaesitosaurus were titanosaurs rather than diplodocoids, but rejected the validity of Nemegtosauridae and the clade concepts given under that name.  Quaesitosaurus  was placed in the Saltasaurinae and Nemegtosaurus in a new, unnamed "Rapetosaurus clade" (which, under ICZN rules, would, if named, be termed subfamily Nemegtosaurinae or tribe Nemegtosaurini, depending on its position). Opisthocoelicaudia was placed in a separate clade, the Opisthocoelicaudiinae.  All three clades are included  in the  Saltasauridae (= Titanosauridae).

In a paper discussing new anatomical data on the skull of Tapuiasaurus, Wilson and his colleagues cast doubt on the monophyly of Nemegtosauridae, judging from a rescoring of the Zaher et al. 2011 cladistic analysis regarding cranial characters. Tapuiasaurus was recovered as basal to Lithostrotia, rendering its position within Nemegtosauridae questionable. A 2014 cladistic analysis gleaning new anatomical data from Diamantinasaurus also rendered Nemegtosauridae paraphyletic, with Rapetosaurus falling out as a member of Saltasauridae closer to Isisaurus than to Nemegtosaurus. The cladistic analysis of Patagotitan recovered Tapuiasaurus as the sister taxon of Rapetosaurus and Isisaurus but not Nemegtosaurus.

Phylogeny

The cladogram below follows Zaher et al. (2011).

References

Sources
 McIntosh, J. S., 1990, "Sauropoda" in The Dinosauria, Edited by David B. Weishampel, Peter Dodson, and Halszka Osmólska. University of California Press, pp. 345–401.
 
 
 Upchurch, P., Barrett, P.M. and Dodson, P. 2004. Sauropoda. In The Dinosauria, 2nd edition. D. Weishampel, P. Dodson, and H. Osmólska (eds.). University of California Press, Berkeley. pp. 259–322.

External links
 Re: Family Nemegtosauridae

 
Category:Lithostrotians