THE BRAINCASE OF THE EARLY ARCHOSAURIAN REPTILE ERYTHROSUCHUS-AFRICANUS

The first detailed description of the braincase of the Triassic early archosaurian reptile Erythrosuchus is presented. Features plesiomorphi c for archosaurs that are described include an ossified laterosphenoid , a 'semilunar depression', posteroventrally positioned internal carot id foramina, a basisphenoid 'inter-tuberal plate', an un- or incomplet ely ossified medial wall of the otic capsule and channel for the peril ymphatic duct, a metotic foramen undivided by bone, and a short lagena r recess. Among the earliest archosaurs, the braincase of Erythrosuchu s is considered to share more derived similarities with the erythrosuc hid Shansisuchus than with other taxa, although further study is requi red to ascertain whether these similarities are homologous. An underst anding of non crown-group archosaur morphology is important for resolv ing controversial questions of homology concerning braincase features in extant archosaurs, as well as for improving estimates of archosaur phylogeny. The most recent common ancestor of crocodiles and birds is hypothesized to have lacked a 'semilunar depression' and basisphenoid 'intertuberal plate', and to have had laterally positioned internal ca rotid foramina, a short lagena, an undivided metotic foramen, an unoss ified eustachian system, and elements of the tympanic cavity that were not pneumatized.