An abelisauroid dinosaur from the Middle Jurassic of Laurasia and its implications on theropod palaeobiogeography and evolution

摘要: Abstract We review here the phylogenetic relationships of a theropod distal end tibia (MB. R.2351) from Middle Jurassic Stonesfield Slate (Taunton Formation, middle Bathonian) Oxfordshire, England. This specimen was previously described as small basal tetanuran, but our reinterpretation suggests that it an early member Abelisauroidea. The new assignment is supported by presence apomorphic vertical facet for reception ascending process astragalus, sub-rectangular anterior scar astragalar process, median ridge in and posterolateral not distinctly offset lateral margin shaft. In particular, shares overall morphology unique combination apomorphies with Australian abelisauroid Ozraptor . Nevertheless, both specimens differ some punctual features. MB. R.2351 constitutes oldest evidence outside Gondwana indicates group had achieved Pangean distribution during, at least, Jurassic. Thus, initial diversification abelisauroids would have occurred earlier than thought. Accordingly, Late implies absence Cretaceous Asiamerican assemblages reflect regional extinction, which competitive replacement coelurosaurs (e.g. tyrannosauroids) surely one hypotheses should be tested future studies.