Nemegtosauridae
Nemegtosauridae is a family of titanosaurian sauropod dinosaurs known chiefly from their distinctive skulls. Its core members are Nemegtosaurus and Quaesitosaurus of the Late Cretaceous of Mongolia, with Rapetosaurus (Wilson, 2005) and Tapuiasaurus (Zaher and colleagues, 2011) sometimes included, although a restudy of its skull treats Tapuiasaurus as a basal titanosaur (Wilson and colleagues, 2016); the group is generally defined as all titanosaurs more closely related to Nemegtosaurus than to Saltasaurus. Its members have long, low skulls bearing slender, peg-like teeth crowded at the front of the jaws, a build that superficially resembles the diplodocids and long obscured their true relationships. For decades these animals were classified among the diplodocoids, but cladistic work has since placed them firmly within Titanosauria. The family's monophyly remains contested, as several analyses instead scatter its members across the titanosaur tree, and the skull of Nemegtosaurus has even been proposed to belong to the otherwise-headless Opisthocoelicaudia.
Under dispute
The monophyly and content of Nemegtosauridae are contested. Wilson (2005) refers Nemegtosaurus and Quaesitosaurus to Nemegtosauridae, a clade of derived titanosaurs, but most trees in the reanalysis of Wilson and colleagues (2016) break up the family, and Nemegtosaurus has been speculated to be the skull of the otherwise-headless Opisthocoelicaudia, a hypothesis Wilson (2005) considers untestable until associated skull and body material is found. The family is placed within Saltasauroidea, following Wilson's (2002) recovery of a clade uniting Nemegtosauridae and Saltasauridae among derived titanosaurs, with its monophyly flagged as unresolved.
Diagnosis
- Low, elongate skull with a long preorbital region
- Slender, peg-like teeth concentrated at the front of the jaws
- Posteriorly retracted external nares
- Frontals excluded from the margin of the supratemporal fenestra
Genera placed directly in Nemegtosauridae
- Nemegtosaurus Maastrichtian (72.2–66.0 Ma)Mongolia
- Quaesitosaurus Campanian (83.6–72.2 Ma)Mongolia
References
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Upchurch, P. (1995). The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London B 349(1330): 365-390. doi:10.1098/rstb.1995.0125
Erected Nemegtosauridae.
upchurch1995a -
Wilson, J. A. (2002). Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136(2): 215-275. doi:10.1046/j.1096-3642.2002.00029.x
Recovered Nemegtosauridae (Nemegtosaurus and Rapetosaurus) in a clade with Saltasauridae within Titanosauria.
wilson2002a -
Wilson, J. A. (2005). Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology 3(3): 283-318. doi:10.1017/s1477201905001628
Redescribed Nemegtosaurus and defended its placement in Nemegtosauridae among derived titanosaurs.
wilson2005a -
Zaher, H.; Pol, D.; Carvalho, A. B.; Nascimento, P. M.; Riccomini, C.; Larson, P.; Juárez Valieri, R. D.; Pires-Domingues, R.; da Silva, N. J.; de Almeida Campos, D. (2011). A Complete Skull of an Early Cretaceous Sauropod and the Evolution of Advanced Titanosaurians. PLoS ONE 6(2): e16663. Public Library of Science (PLoS). doi:10.1371/journal.pone.0016663
Described Tapuiasaurus and recovered it in Nemegtosauridae, closer to Rapetosaurus than to Nemegtosaurus.
zaher2011a -
Wilson, J. A.; Pol, D.; Carvalho, A. B.; Zaher, H. (2016). The skull of the titanosaur Tapuiasaurus macedoi (Dinosauria: Sauropoda), a basal titanosaur from the Lower Cretaceous of Brazil. Zoological Journal of the Linnean Society 178(3): 611-662. Oxford University Press (OUP). doi:10.1111/zoj.12420
Restudied the skull of Tapuiasaurus as a basal titanosaur; with it rescored and new Isisaurus data added, the original matrix no longer recovers the three nemegtosaurids together.
wilson2016a