Re-assessment of a large archosaur dentary from the Late Triassic of South Wales, United Kingdom

Abstract

A large jaw of a predatory archosaur from the latest Triassic of South Wales, named Zanclodon cambrensis, has long intrigued vertebrate palaeontologists. Could it be the oldest large theropod dinosaur? Here we reanalyse the specimen based on a new 3D digital reconstruction. We confirm first that it is indeed latest Triassic in age, most likely extracted from sandstones of the Cotham Member of the Lilstock Formation (Penarth Group, Rhaetian). Anatomically it shows features of theropod dinosaurs rather than other large non-dinosaurian predatory archosaurs of the Triassic. It shares general characteristics with European coelophysoids of similar age such as Liliensternus and Dracoraptor but is considerably larger. It is not a megalosauroid, as suggested previously, but it is unclear whether it might be an averostran or tetanuran. Its close similarity to Dilophosaurus suggests that this left-hand mandible specimen represents a more derived basal neotheropod and we assign it to a new genus, as Newtonsaurus cambrensis.