Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland

Erpetosuchus, a small archosaurian reptile from the Late Triassic of Scotland and North America, has often been implicated in the ancestry of crocodilians. A restudy of the type specimen, using new high-fidelity casts, as well as examination of new, hitherto undescribed material, allows a detailed description and restoration of Erpetosuchus granti from the Lossiemouth Sandstone Formation (late Carnian, Late Triassic). This small reptile is known only from the front end of its body; a complete skull, cervical vertebral column, anterior dorsals and ribs, shoulder girdle, and forelimb. The skull shows a number of unusual features: a reduced row of only 4-5 teeth on the anterior part of the maxilla, a large antorbital fenestra set in a deep fossa whose margins are marked by distinct sharply angled ridges, a jugal that is divided into a lateral and a ventral portion by a sharp ridge, a deeply recessed tympanic area, the angular and surangular marked by a strong ridge running back from the ventral margin of the mandibular fenestra, and teeth oval in cross-section and lacking anterior and posterior carinae and marginal serrations. The remains suggest that Erpetosuchus was a light, cursorial animal that may have fed on insects. A cladistic analysis of crurotarsan archosaurs indicates that Erpetosuchus is the closest sister group of Crocodylomorpha among known basal archosaurs. It shares with them a deep recess in the cheek region framed by the quadrate and quadratojugal which slope forward side-by-side at an angle of 45degrees above horizontal, and reach the upper margin of the lower temporal fenestra. In Erpetosuchus the recess is entirely lateral, while in crocodylomorphs, the recess penetrates medially as well, since the quadrate/quadratojugal bar meets the side wall of the braincase. (C) 2002 The Linnean Society of London.