Data from: Cranial remains of Ramsayia magna from the Late Pleistocene of Australia and the evolution of gigantism in wombats (Vombatidae; Marsupialia)

Giant wombats (defined here as body mass ≥ 70 kg) are found in the genera Phascolonus, Ramsayia, and perhaps also Sedophascolomys. Of these, Ramsayia is the currently the most poorly known, having been described from fragmentary mandibular and cranial fragments. Here, we report the most complete cranial remains attributable to the genus, identified as the species R. magna. The remains provide new important insights into the anatomy of the species and the evolutionary adaptations to gigantism in Vombatidae. We record parietal sinuses in a vombatid for the first time, an adaptation to increased skull size relative to the braincase. The presence of a prominent premaxillary spine may indicate the species possessed a large, fleshy nose. Both of features are convergent on other large-bodied, non-vombatid extinct megaherbivores of Australia such as Diprotodon optatum. We use the cranial remains to examine the phylogenetic relationships of the giant wombats to other vombatids. Phylogenetic analysis using maximum parsimony and Bayesian inference indicates that Phascolomys, Ramsayia, and Sedophascolomys form a clade, suggesting a single origin of gigantism within Vombatidae. This origin may have been related to the exploitation of poor-quality foods by these taxa, and preceded the extreme specialisations observed in the incisor and cranial anatomy of the giant wombats. U-series and combined U-series and Electron Spin Resonance (ESR) dating methods were applied to one fossil tooth. All sources of uncertainty considered, age calculations systematically correlate the fossil remains to Marine Isotope Stage 5, and an age of approximately 80,000 years can be proposed for this specimen. With only a single well dated occurrence for this taxon, it is currently impossible to determine when and why R. magna became extinct.