The braincase of the early archosaurian reptile Erythrosuchus africanus

The fimt detailed description of the braincase of the Triassic early archosaurian reptile Elythrosuchus is presented. Features plesiomorphic for archosaurs that are described include an ossified laterosphenoid, a ‘semilunar depression’, posteroventrally positioned internal carotid foramina, a basisphenoid ‘intertuberal plate’, an un‐ or incompletely ossified medial wall of the otic capsule and channel for the perilymphatic duct, a metotic foramen undivided by bone, and a short lagenar recess. Among the earliest archosaurs, the braincase of Erythrosuchus is considered to share more derived similarities with the erythrosuchid Shansisuchus than with other taxa, although further study is required to ascertain whether these similarities are homologous. An understanding of non crown‐group archosaur morphology is important for resolving 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 carotid foramina, a short lagena, an undivided metotic foramen, an unossified eustachian system, and elements of the tympanic cavity that were not pneumatized.