The basicranium of a basal prosauropod from the Euskelosaurus range zone and thoughts on the origin of dinosaurs

The basicranium of a basal prosauropod from the Euskelosaurus range zone of South Africa (NMQR 3314) is characterised by a wide basal fissure between the basioccipital and the basisphenoid-basiparasphenoid. The basioccipital and the atlantal intercentrum form a large horizontal plate which extends v entral to the occipital condyle and dorsal to the much expanded medial marg ins of the retroarticular processes of the rami of the lower jaw. The prese nce of the basal fissure in the basicranium of NMQR 3314 appears to represe nt a transitional condition between the median eustachian systems of primit ive aquatic archosauromorphs, such as Proterosuchus and phytosaurs, and tha t of the earliest terrestrial prosauropods. The basicranial morphology of N MQR 3314 seems to illustrate a functionally very important stage in the evo lution of early dinosaurs. (C) 1999 Elsevier Science Limited. rights reserv ed.