Austrosaurus mckillopi was the first Cretaceous sauropod reported from Australia, and the first Cretaceous dinosaur reported from Queensland (northeast Australia). This sauropod taxon was established on the basis of several fragmentary presacral vertebrae (QM F2316) derived from the uppermost Lower Cretaceous (upper Albian) Allaru Mudstone, at a locality situated 77 km west-northwest of Richmond, Queensland. Prior to its rediscovery in 2014, the type site was considered lost after failed attempts to relocate it in the 1970s. Excavations at the site in 2014 and 2015 led to the recovery of several partial dorsal ribs and fragments of presacral vertebrae, all of which clearly pertained to a single sauropod dinosaur. The discovery of new material of the type individual of Austrosaurus mckillopi, in tandem with a reassessment of the material collected in the 1930s, has facilitated the rearticulation of the specimen. The resultant vertebral series comprises six presacral vertebrae—the posteriormost cervical and five anteriormost dorsals—in association with five left dorsal ribs and one right one. The fragmentary nature of the type specimen has historically hindered assessments of the phylogenetic affinities of Austrosaurus, as has the fact that these evaluations were often based on a subset of the type material. The reappraisal of the type series of Austrosaurus presented herein, on the basis of both external morphology and internal morphology visualized through CT data, validates it as a diagnostic titanosauriform taxon, tentatively placed in Somphospondyli, and characterized by the possession of an accessory lateral pneumatic foramen on dorsal vertebra I (a feature that appears to be autapomorphic) and by the presence of a robust ventral mid-line ridge on the centra of dorsal vertebrae I and II. The interpretation of the anteriormost preserved vertebra in Austrosaurus as a posterior cervical has also prompted the re-evaluation of an isolated, partial, posterior cervical vertebra (QM F6142, the ‘Hughenden sauropod’) from the upper Albian Toolebuc Formation (which underlies the Allaru Mudstone). Although this vertebra preserves an apparent unique character of its own (a spinopostzygapophyseal lamina fossa), it is not able to be referred unequivocally to Austrosaurus and is retained as Titanosauriformes indet. Austrosaurus mckillopi is one of the oldest known sauropods from the Australian Cretaceous based on skeletal remains and potentially provides phylogenetic and/or palaeobiogeographic context for later taxa such as Wintonotitan wattsi, Diamantinasaurus matildae and Savannasaurus elliottorum.
The sauropod taxon Austrosaurus mckillopi is of historical significance to Australian palaeontology as the first Cretaceous dinosaur recognized in Queensland, and the first Cretaceous sauropod ever reported from the entire continent. The augmentation, articulation and description of the type material have helped to shed light on the phylogenetic position of Austrosaurus, unequivocally placing it within Titanosauriformes, and probably as a member of Somphospondyli. The identification of an autapomorphic auxiliary pneumatic foramen in dorsal vertebra I means that the referral of other sauropod specimens to Austrosaurus should be possible in the future, although this feature is not presently observable in any other Australian sauropod specimen. The morphological congruence of the posteriormost cervical vertebra of Austrosaurus with QM F6142 (the ‘Hughenden sauropod’) might represent grounds for the referral of the latter to the former, although this can not be demonstrated unequivocally. Lastly, despite its fragmentary nature, Austrosaurus appears to share several features with the type specimens of both Diamantinasaurus and Savannasaurus, possibly indicating a close phylogenetic relationship.
The fragmentary nature of the type series of Austrosaurus has impeded, and will continue to restrict, efforts to precisely resolve its phylogenetic position within Titanosauriformes. Consequently, the palaeobiogeographic significance of Austrosaurus is poorly understood, a situation worsened by the relative rarity of Early Cretaceous titanosauriforms in South America and the lack of such in Antarctica. Nevertheless, the presence of numerous titanosauriform lineages in the Early Cretaceous of South America provides some context for Australian Early Cretaceous titanosauriforms like Austrosaurus, and also for the mid-Cretaceous Winton Formation fauna, which appears to have been dominated by titanosaurs with amphicoelous (rather than procoelous) caudal vertebrae.
Stephen F. Poropat, Jay P. Nair, Caitlin E. Syme, Philip D. Mannion, Paul Upchurch, Scott A. Hocknull, Alex G. Cook, Travis R. Tischler and Timothy Holland. 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. DOI: 10.1080/03115518.2017.1334826