Wednesday, January 2, 2019
Did lognkosaurs originate in Laurasia?
Last year yielded a number of surprises and new developments in terms of sauropod biogeography, including the description of the youngest sauropod from mainland Africa (Mansourasaurus), the erection of Maraapunisaurus for the apocryphal gigantic sauropod Amphicoelias fragillimus, and the description of the first diplodocoid from East Asia (Lingwulong). Therefore, why not start off the new year with a post about titanosaur biogeography?
Averianov and Efimov (2018) describe the new titanosaur taxon Volgatitan simbirskiensis from Early Cretaceous (Hauterivian) marine shale deposits along the banks of the Volga River in Ulyanovsk Province, European Russia, making this taxon the oldest record of a titanosaur from Laurasia. In their phylogenetic analysis, the authors recover this taxon as sister to the titanosaur clade Lognkosauria, which is exclusively known from Patagonia (the Asian form Ruyangosaurus is considered a member of Lognkosauria by Sassani and Bivens 2017) On the other hand, the same authors recover another titanosaur taxon from European Russia, Tengrisaurus, as a member of Saltasauridae.
The phylogenetic results for Volgatitan obtained by Averianov and Efimov (2018) raise questions about whether the clade Lognkosauria evolved in Gondwana during the early Cretaceous or branched out into Gondwana from Laurasia later in the Early Cretaceous. Until recently, all bonafide lognkosaurians were known from Late Cretaceous deposits in Patagonia, including the recently described taxon Patagotitan, but Sassani and Bivens (2017) extended the geographic range of Lognkosauria to Laurasia by recovering the Aptian-Albian form Ruyangosaurus from Henan Province, eastern China as a sister-taxon of Puertasaurus. When discussing the results of the phylogenetic analysis of Volgatitan, Averianov and Efimov considered it likely that Lognkosauria had a widespread geographic distribution until the Late Cretaceous, when representatives of the group became confined to South America. They discounted the likelihood of a South American origin for Lognkosauria given the absence of members of this clade from South America before the Albian period. At first glance, it may be prudent to accept the conclusions by Averianov and Efimov (2018) that early lognkosaurs had a Laurasian origin in the Early Cretaceous given the age of Volgatitan as well as Ruyangosaurus.
Although the East African taxon Malawisaurus is often recovered as the basalmost lithostrotian by multiple phylogenetic analyses (e.g. Upchurch et al. 2004; Poropat et al. 2014; Averianov and Efimov 2018), the cladogram of Sassani and Bivens (2017) recovers Malawisaurus as more closely related to members of Lognkosauria, rather than at the base of Lithostrotia, suggesting that early lognkosaurians, or at least close relatives of the group, were widespread globally during the Early Cretaceous. Averianov and Efimov (2018) put the body mass estimate of Volgatitan at 38,157 pounds (17,308 kg) and Paul (2010) gives the weight for Malawisaurus as 22,000 pounds (10,000 kg), far lower than the body mass estimates for Patagonian lognkosaurs, suggesting that some Early Cretaceous lognkosaur relative from Gondwana may have dispersed into Laurasia to either develop dwarfism in insular environments or resort to gigantism in response to phytobiotic factors like tall gymnosperms. Given the dearth of titanosaur remains from the earliest Cretaceous (the genus Triunfosaurus from the Berriasian-Valanginian of Brazil was assigned to Titanosauria by Carvalho et al. 2017, but its placement was questioned by Poropat et al. 2017), but also the age of Malawisaurus and Ruyangosaurus, it seems highly parsimonious to conclude that the earliest lognkosaurs originated in Gondwana during the Early Cretaceous and dispersed to other parts of the world in that time frame, eventually developing gigantism later in the Cretaceous due to environmental influences.
Averianov, A. and Efimov, V. 2018. The oldest titanosaurian sauropod
of the Northern Hemisphere. Bio. Comm. 63(3): 145–162. https://doi.org/10.21638/spbu03.2018.301
Carvalho, I.D.S., Salgado, L., Lindoso, R.M., Araujo-Junior, H.I.D., Noguiera, F.C.C. & Soares, J.A., 2017. A new basal titanosaur (Dinosauria, Sauropoda) from the Lower Cretaceous of Brazil. Journal of South American Earth Sciences 75: 74–84.
Paul, G.S, 2010. The Princeton Field Guide to Dinosaurs. Princeton: Princeton University Press.
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Mannion, P.D.; Hocknull, S.A.; Kear, B.P.; Sloan, T.; Sinapius, G.H.K.;
Elliott, D.A., 2014. Revision of the sauropod dinosaur Diamantinasaurus matildae
Hocknull et al. 2009 from the mid-Cretaceous of Australia: Implications for
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Poropat, S.F., Nair, J.P., Syme, C.E., Mannion, P.D., Upchurch, P., Hocknull, S.A., Cook, A.G., Tischler, T.R., and Holland, T., 2017. Reappraisal of Austrosaurus mckillopi Longman, 1933 from the Allaru Mudstone of Queensland, Australia’s first named Cretaceous sauropod dinosaur. Alcheringa: An Australasian Journal of Palaeontology 41:4, 543-580, DOI: 10.1080/03115518.2017.1334826
2017. The Chinese colossus: an evaluation of the phylogeny of Ruyangosaurus giganteus and its implications for titanosaur evolution. PeerJ Preprints
Upchurch, P., Barrett, P. M., and
Dodson, P. 2004. Sauropoda. pp. 259−322 in: The Dinosauria. Second Edition,
edited by Weishampel, D. B., Dodson, P., and Osmolska, H. Berkeley, Los
Angeles, London: University of California Press.
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