Abstract
The diversity of Australia’s theropod fauna from the ‘mid’-Cretaceous (Albian–Cenomanian) is distinctly biased towards the medium-sized megaraptorids, despite the preponderance of abelisauroids in the younger but latitudinally equivalent Patagonian theropod fauna. Here, we present new evidence for the presence of ceratosaurian, and specifically abelisauroid, theropods from the Cenomanian Griman Creek Formation of Lightning Ridge, New South Wales. A partial cervical vertebra is described that bears a mediolaterally concave ventral surface of the centrum delimited by sharp ventrolateral ridges that contact the parapophyses. Among theropods, this feature has been reported only in a cervical vertebra attributed to the noasaurid Noasaurus. We also reappraise evidence recently cited against the ceratosaurian interpretation of a recently described astragalocalcaneum from the upper Barremian–lower Aptian San Remo Member of the upper Strzelecki Group in Victoria. Inclusion of the Lightning Ridge cervical vertebra and Victorian astragalocalcaneum into a revised phylogenetic analysis focused on elucidating ceratosaurian affinities reveals support for placement of both specimens within Noasauridae, which among other characters is diagnosed by the presence of a medial eminence on the ascending process of the astragalus. The Lightning Ridge and Victorian specimens simultaneously represent the first noasaurids reported from Australia and the astragalocalcaneum is considered the earliest known example of a noasaurid in the world to date. The recognition of Australian noasaurids further indicates a more widespread Gondwanan distribution of the clade outside of South America, Madagascar and India consistent with the timing of the fragmentation of the supercontinent.
Highlights
The diversity of Australia’s theropod fauna from the ‘mid’-Cretaceous (Albian–Cenomanian) is distinctly biased towards the medium-sized megaraptorids, despite the preponderance of abelisauroids in the younger but latitudinally equivalent Patagonian theropod fauna
The majority of documented theropod remains from Australia are from the ‘mid’-Cretaceous (Albian–Cenomanian) and pertain predominantly to megaraptorids[1,2,3,4,5,6,7], an exclusively Gondwanan clade of theropods initially interpreted as a member of Allosauroidea[2]
Despite the preponderance of megaraptorids in ‘mid’-Cretaceous Australia, a diverse high palaeo-latitude theropod fauna has been hypothesised within the upper Barremian–lower Albian deposits on the south coast of Victoria, including megaraptorans[3,5,14], ceratosaurs[15], spinosaurids[16], tyrannosauroids[3,17], possible unenlagiine dromaeosaurids and indeterminate maniraptoriforms[3]
Summary
The diversity of Australia’s theropod fauna from the ‘mid’-Cretaceous (Albian–Cenomanian) is distinctly biased towards the medium-sized megaraptorids, despite the preponderance of abelisauroids in the younger but latitudinally equivalent Patagonian theropod fauna. On this basis, it was suggested that the Australian tibia represented a member of Abelisauroidea[19]. It was suggested that the Australian tibia represented a member of Abelisauroidea[19] This interpretation was maintained in a reassessment of a theropod distal tibia from the Middle Jurassic of England[20], which concluded that a depressed and subdivided facet for the astragalar ascending process was a synapomorphy of Abelisauroidea. It was subsequently suggested that the evidence for referral of NMV P221202 to Ceratosauria was weak, and that it could only be considered as an indeterminate averostran at best[8]
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