Skull anatomy of Mussaurus patagonicus (Dinosauria: Sauropodomorpha) from the Late Triassic of Patagonia

Abstract

The skull anatomy of Mussaurus patagonicus from the Upper Triassic Laguna Colorada Formation is described based on a revision of the type material and several recently found specimens. The studied material include two distinct size classes of individuals. The type material consists of extremely young individuals whereas the new specimens are interpreted as juvenile or subadult individuals. The latter are significantly larger, having a skull approximately three times longer than the type material. The skull anatomy of this taxon shows derived characters shared with some basal sauropodomorphs and eusauropods, which are absent in other basal sauropodomorphs (e.g. Thecodontosaurus, Plateosaurus). These include the presence of an extension of the infratemporal fenestra ventral to the orbit, dorsal and anterior rami of quadratojugal subperpendicular to each other, dorsoventral expansion of dentary at mandibular symphysis, slightly procumbent teeth with broad serrations restricted to the apical region (absent in some teeth). Differences among the studied specimens helps to understand the early ontogenetic changes occurring in this basal sauropodomorph, revealing major changes in the rostral and temporal regions.