Nemegtosauridae
| Nemegtosaurids Temporal range: Early Cretaceous - Late Cretaceous, 117–66 Ma |
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| Skeleton of a juvenile Rapetosaurus krausei, Field Museum of Natural History | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | Saurischia |
| Suborder: | †Sauropodomorpha |
| Clade: | †Neosauropoda |
| Clade: | †Macronaria |
| Clade: | †Titanosauria |
| Clade: | †Lithostrotia |
| Family: |
†Nemegtosauridae Upchurch, 1995 |
| Genera | |
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.
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), Upchurch et al. (2004.
Wilson in 2002 referred the two genera to the family Nemegtosauridae, and on the basis of cladistic analysis, transferred them 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).
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