The skull of the Early Triassic archosauromorph reptile Prolacerta broomi and its phylogenetic significance

Description of new and re-examination of previously described cranial remains of Prolacerta broomi Parrington allows reappraisal of the structure of the skull in this basal archosauromorph reptile. The ventral margin of the premaxilla is slightly deflected, and there is a relatively large lateral foramen in the maxilla that is bounded anteriorly by the premaxilla; both features are shared with the basal rhynchosaur Mesosuchus and the basal archosauriform Proterosuchus. Implantation of the marginal dentition is ankylothecodont: the teeth are rooted relatively deeply, bounded lingually by a deep wall of the jaw, and anchored to the jaw by bone of attachment. The pineal foramen varies in size from little more than a scar in the interparietal suture to a suboval opening several millimetres in diameter. Contrary to previous claims, the skull roof in Prolacerta was akinetic and quadrate mobility (streptostyly) was absent. Phylogenetic analysis of a previously published data matrix, modified by the addition of new anatomical data and reinterpretation of some characters, corroborates the hypotheses of the polyphyly of Prolacertiformes (Protorosauria) and of a close relationship between Prolacerta and Archosauriformes. (C) 2004 The Linnean Society of London, Zoological Journal of the Linnean Society.