Nemegtosauridae

Nemegtosaurids
Temporal range: Early Cretaceous - Late Cretaceous, 117–66 Ma
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.

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), 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.[1]

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).[2]

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.[3] For her part, Kristina Curry Rogers (see also Cuury Rogers and Forster [2001][4]) 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).[5]

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. Because Tapuiasaurus is recovered as basal to Lithostrotia, its position within Nemegtosauridae remains questionable.[6] 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.[7]

Phylogeny

The cladogram below follows Zaher et al. (2011).[8]

Lithostrotia 

Malawisaurus
Nemegtosauridae 

Nemegtosaurus

Rapetosaurus

Tapuiasaurus

Isisaurus

Diamantinasaurus


Saltasauridae 
Opisthocoelicaudiinae 

Alamosaurus

Opisthocoelicaudia



Saltasaurinae 

Neuquensaurus

Saltasaurus








References

  1. ↑ Wilson JA. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136: 217–276.
  2. ↑ Apesteguıa S. 2004. Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia. Naturwissenschaften 91: 493–497.
  3. ↑ Wilson JA. 2005. Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology 3: 283– 318.
  4. ↑ Curry Rogers, K. and Forster, C.A. 2001. The last of the dinosaur titans: a new sauropod from Madagascar. Nature, 412:520-534.
  5. ↑ Curry Rogers K. 2005. Titanosauria. In: Curry Rogers KA, Wilson JA, eds. The sauropods: evolution and paleobiology. Berkeley: University of California Press, 50–103.
  6. ↑ Wilson, J. A., Pol, D., Carvalho, A. B. and 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. doi: 10.1111/zoj.12420
  7. ↑ Poropat, S.F.; Upchurch, P.; Mannion, P.D.; Hocknull, S.A.; Kear, B.P.; Sloan, T.; Sinapius, G.H.K.; Elliot, D.A. (2014). "Revision of the sauropod dinosaur Diamantinasaurus matildae Hocknull et al. 2009 from the mid-Cretaceous of Australia: Implications for Gondwanan titanosauriform dispersal". Gondwana Research. doi:10.1016/j.gr.2014.03.014.
  8. ↑ Hussam Zaher, Diego Pol, Alberto B. Carvalho, Paulo M. Nascimento, Claudio Riccomini, Peter Larson, Rubén Juarez-Valieri, Ricardo Pires-Domingues, Nelson Jorge da Silva Jr., Diógenes de Almeida Campos (2011). "A Complete Skull of an Early Cretaceous Sauropod and the Evolution of Advanced Titanosaurians". PLoS ONE. 6 (2): e16663. doi:10.1371/journal.pone.0016663. PMC 3034730Freely accessible. PMID 21326881.

Sources

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