Systematics of Carnivorous Ornithodirans from the 'Mid'-Cretaceous Griman Creek Formation, Lightning Ridge, and Quantitative Considerations for Evaluating Morphology in Dinosaurs

Abstract

<p>The diversity of Australian Mesozoic reptiles, in particular theropods and pterosaurs, is arguably the least well known and sampled of any continental assemblage in the world. These limitations continue to hinder evaluations of their phylogenetic and biogeographic affinities. The Cenomanian Griman Creek Formation at Lightning Ridge, central-north New South Wales constitutes one of the richest Australian terrestrial ecosystems, yet has remained largely unstudied until relatively recently. Therefore, new fossil discoveries from this region have the potential to contribute to our understanding of Australia’s theropods and pterosaurs. An investigation identifies new specimens from Lightning Ridge pertaining to Avetheropoda, among which is only the third associated theropod reported from Australia, and the first vertebral elements of a megaraptorid from Lightning Ridge. The enigmatic basal theropod clade Noasauridae is reported for the first time in Australia based on a cervical vertebra from Lightning Ridge, and a previously-described astragalocalcaneum from the Aptian–Albian Eumeralla Formation of southern Victoria. Isolated teeth pertaining to Anhangueria are described, marking the first published record of pterosaurs in New South Wales. The diversity of theropods in Australia is evaluated from the fossil tooth record using a combination of traditional descriptive methods and the application of Linear Discriminant Analysis; both methods come to agreement on the preponderance of megaraptorids in Australia, and also identify the presence of unenlagiine dromaeosaurids in southern Victoria. Finally, a novel complication in the characterisation of macroevolutionary patterns resulting from the ordination of discrete character data is recognised for the first time. Specifically, a statistically significant correlation between the body size of dinosaurs with morphospace variables calculated from the Principal Coordinate Analysis is described. The implications of this correlation are demonstrated in a re-analysis of data relating to a macroevolutionary hypothesis of the assembly of the avian body plan and a method is described for the removal of body mass as a confounding factor.</p>