SAMA P40536
Project
ID: 000392635
Public
Australian dinosaur research has undergone a renaissance in the last ten years, with growing knowledge of mid-Cretaceous assemblages revealing an endemic high-paleolatitude Gondwanan fauna. One of its most conspicuous members is ankylosaurs, which are rare but nonetheless occur in most Australian dinosaur-bearing formations spanning the uppermost Barremian to lower Cenomanian. Here we describe a partial ankylosaur skull from the marine Toolebuc Formation exposed at Boulia in western Queensland, Australia. This skull represents the oldest ankylosaurian material from Queensland, predating the holotype of Kunbarrasaurus ieversi, which was found in the overlying Allaru Mudstone. The ankylosaur skull is encased in a limestone concretion with the maxillary tooth rows preserved only as impressions. Synchrotron radiation X-ray tomography was used to non-destructively image the specimen and facilitate virtual preparation of the separate cranial bones. Tomographic scans revealed the vomer, palatines, sections of the ectopterygoids, maxillae, and multiple teeth. Significantly, these elements are not fully observable in the holotype of K. ieversi. Thus, our new tomographic data sheds light on both the osteology and phylogenetic relationships of the taxon. The vomer is anteroposteriorly elongated, becoming mediolaterally expanded and bulbous anteriorly. There is no fusion between the vomer and surrounding palatal skeleton, although it is closely associated with the palatines posteriorly. The palatines are angled anteroventrally, and together with the ectopterygoid, form the posterior margin of the choanae. The teeth have 6–7 denticles, similar to K. ieversi and other nodosaurids, but unlike the 10–11 denticles observed in ankylosaurid teeth from the upper Strzelecki Group of Victoria in southeastern Australia. A prominent cingulum is preserved on the labial facet and, in some teeth, is also present on the lingual facet. The lingual cingulum is apical to its labial counterpart, as seen in nodosaurids. The phylogenetic analysis places the ankylosaur skull as the sister taxon of K. ieversi, prompting taxonomic referral to cf. Kunbarrasaurus sp. The Boulia cf. Kunbarrasaurus sp. skull thus elucidates aspects of palatal morphology in Australian ankylosaurs and highlights one of the most ubiquitous components of Australian mid-Cretaceous dinosaur faunas.