Osteology of Leptopleuron lacertinum Owen, a procolophonoid parareptile from the Upper Triassic of Scotland, with remarks on ontogeny, ecology and affinities

Abstract

The Late Triassic reptile Leptopleuron lacertinum Owen, 1851 is described for the first time in full anatomical detail, based on newly produced silicone and plastic casts of the numerous specimens preserved as natural moulds. Previously, only the braincase has been described from these detailed casts. Leptopleuron is reconstructed as a 270-mm-long reptile with a long tail, although it is possible that even the largest known specimens were still sub-adults. Within Procolophonoidea, Leptopleuron is distinguished by the following non-braincase autapomorphies: two flattened, triangular spines of equal size on the quadratojugal; V-shaped groove on the jugal; the anterior tip of the jugal in contact with the posterolateral extension of the nasal; minimal contact between the jugal and the postorbital; frontals narrow anterior to the orbitotemporal openings; the vomerine dentition consisting of a tall and a short pair of fangs; broad medial ridge of pleurocentra of the dorsal vertebrae divided into three separate ridges by two deep grooves on each pleurocentrum; distinct three-fold depression pattern on the ventral side of ischium; and the first phalanx on the fifth pedal digit being long and slim. Leptopleuron shares some features with living sand lizards and might have lived a burrowing lifestyle. The dentition and body shape of Leptopleuron imply it ate a diet of fibrous plant material or hard-shelled invertebrates.