Material referred to Megalosaurus (Dinosauria: Theropoda) from the Middle Jurassic of Stonesfield, Oxfordshire, England: one taxon or two?

Megalosaurus bucklandii von Meyer, 1832 is one of the most widely known, but poorly understood, of all theropod dinosaurs. It was recently claimed that the large theropod material from the Stonesfield Slate of Oxfordshire, which is usually attributed solely to M. bucklandii, represents not one, but two taxa on the basis of differences in the scapulocoracoids, ilia and femora. Here we evaluate this claim following examination of almost all relevant examples of these elements from the UK. A consistent suite of four differing femoral character states cannot be accounted for by sexual, ontogenetic or individual variation, and supports the presence of two morphotypes that probably represent distinct taxa. However, other purported differences between these two morphotypes are shown to be either ambiguous or erroneous. One taxon (‘morphotype B’, corresponding to that represented by one of the paralectotypes of M. bucklandii) appears to be a basal tetanuran, whereas the other (‘morphotype A’) cannot be confidently assigned to any major theropod clade. Phylogenetic analyses of theropod interrelationships should not include any nominal species of Megalosaurus until a full taxonomic appraisal of this material has been completed.