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.

Supplementary File: We critically assess the morphological characters used by Tedford (2002) in his phylogenetic analysis of Vombatidae, and his character scoring criteria. Character numbers follow Tedford (2002; see also Murray, 1998: table 4). 

Data Files: The fossil specimen (QMF60370) is from Johansen’s Cave, Mt Etna National Park, Queensland, Australia. The specimen is accessioned in the collections of the Queensland Museum, Brisbane, Queensland, Australia. The specimen is stored in a fibreglass cradle for added protection.

The 3D models were made using standard turntable photogrammetry. Due to the fragile nature of the specimen, two separate models were made of the internal and external views, respectively. The specimen was left in the fibreglass cradle at the time of photogrammetry.

Photos were taken with a Nikon D5200 digital SLR camera with F-stop value 22, ISO 320, and focal length 40 mm. The internal view model was made using 288 photos and the external view model with 327 photos. Photos were mostly taken every ca. 10 degree rotation of the turntable to produce rings of images around the specimen. The camera was then elevated by ca. 10 cm and a new ring of images taken. This process was repeated two or three times. Some additional close-up photos were variously taken of key features of the specimen such as teeth.

The photos were then processed using Agisoft Metashape Professional (version 1.6.1 build 10009 64 bit) to produce photogrammetry models. Photos were initially aligned at the ‘highest’ accuracy with a key point limit of 150,000 and tie point limit of 100,000. The dense point cloud was then constructed at ‘ultra high’ quality with ‘aggressive’ depth filtering. Subsequently, the mesh was made on the basis of depth maps at ‘ultra high’ quality, ‘extrapolated’ interpolation, and with a face count of 500,000. Finally, the texture (4096 x 4096 pixels) was constructed using a ‘diffuse map’ with the source data coming from the original photos. Uninformative background artefacts (e.g., the benchtop) were removed digitally before the models were exported into OBJ format (with associated STL and texture files), and 3D PDF, respectively.