Cranial anatomy of Shuvosaurus inexpectatus, an edentulous poposauroid pseudosuchian from the Late Triassic of Texas

Abstract

ABSTRACT Shuvosaurus inexpectatus is an edentulous poposauroid from the late Lacian or earliest Alaunian (Late Triassic) of western Texas, which had been identified primarily from three individuals. A complete repreparation and redescription of the Shuvosaurus cranial elements highlights many of the features that identify it as a poposauroid and a shuvosaurid. Cranial elements unique to Shuvosauridae include an edentulous jaw with a rhamphotheca groove indicating the presence of a beak, a secondary palate formed from the premaxillae and maxillae, and an elongated parabasisphenoid. Shuvosaurus cranial autapomorphies include the articulation of the squamosal and quadratojugal that forms a projection into the posterior edge of the lateral temporal fenestra, the presence of a triangular posterior process of the squamosal, and a basioccipital that is exposed between the exoccipitals, forming the ventral edge of the foramen magnum. In addition to the beak, Shuvosaurus also possessed an extremely large orbit indicating good eyesight, enlarged olfactory bulbs indicating an excellent sense of smell, and enlarged floccular lobes indicating that Shuvosaurus was highly active with good balance and highly developed gaze stabilisation. These cranial adaptations all suggest that Shuvosaurus was not only bipedal but also subsisted on an herbivorous diet.