Revision of the sauropod dinosaur Diamantinasaurus matildae Hocknull et al. 2009 from the mid-Cretaceous of Australia: Implications for Gondwanan titanosauriform dispersal ☆

The osteology of Diamantinasaurus matildae, the most complete Cretaceous sauropod described from Australia to date, is comprehensively reassessed. The preparation of additional material from the type locality, pertaining to the same individual as the holotype, sheds light on the morphology of the axial skeleton and provides additional information on the appendicular skeleton. The new material comprises two dorsal vertebrae, an incomplete sacrum (including four partial coalesced vertebrae), the right coracoid, the right radius, an additional manual phalanx, and a previously missing portion of the right fibula. In this study we identify thirteen autapomorphic characters of Diamantinasaurus, and an additional five characters that are locally autapomorphic within Titanosauriformes. This work provided an opportunity to revisit the phylogenetic placement of Diamantinasaurus. In two independent data matrices, Diamantinasaurus was recovered within Lithostrotia. One analysis resolved Diamantinasaurus as the sister taxon to the approximately coeval Tapuiasaurus from Brazil, whereas the second analysis recovered Diamantinasaurus as the sister taxon to Opisthocoelicaudia from the latest Cretaceous of Mongolia. The characters supporting the recovered relationships are analysed, and the palaeobiogeographical implications of the lithostrotian status of Diamantinasaurus are explored. A brief review of the body fossil record of Australian Cretaceous terrestrial vertebrates suggests close ties to South America in particular, and to Gondwana more generally.