Basal Dinosauriform Remains from Britain and the Diagnosis of the Dinosauria

A new genus and species of dinosauriform is described from the Triassic of south‐west England. The description is based on isolated elements recovered from an assemblage of other dissociated tetrapod remains that include crocodylomorphs, rauisuchiforms and sphenodontians. The key elements in the new taxon are the ilium, astragalus, and the humerus, and these exhibit five synapomorphies of Dinosauria. Three of these, namely a largely to fully perforate acetabulum, the presence of a brevis fossa, and a reduced astragalus with an ascending process, are considered to be particularly relevant. The definition and diagnosis of the Dinosauria are restated and the positions of the new form, herrerasaurs and Eoraptor relative to true dinosaurs are discussed.