The cranial anatomy of the sauropod Turiasaurus riodevensis and implications for its phylogenetic relationships

Abstract

The skull of Turiasaurus is known from a nearly complete posterior section (e.g. braincase, skull roof, quadrates and left mandible) and fragments of the snout (e.g. portions of premaxilla, maxilla, nasal and lacrimal). Skull material of the holotypic individual was discovered in close association. Comparisons with other sauropods suggest that the Turiasaurus skull most closely resembled those of Jobaria, Camarasaurus and Mamenchisaurus youngi, possessing large spatulate teeth, enlarged and partially retracted external nares, and a broadly rounded muzzle. The list of autapomorphies for Turiasaurus is augmented by the new cranial data, including features such as: (1) a shelf-like projection of bone from the medial surface of the distal end of the maxillary ascending process; and (2) a rounded boss-like area on the lateral surface of the jugal. There are also unusual character states, such as the excavation of the posterior surfaces of the basal tubera (present in Turiasaurus and Losillasaurus) that probably have a wider phylogenetic significance. Phylogenetic analyses, using two different datasets, support the view that Turiasaurus, Losillasaurus and Galveosaurus form a monophyletic Turiasauria clade that lies just outside of Neosauropoda. The addition of the new cranial data slightly strengthens the support for this topology, but the relationships of other taxa (such as Jobaria) become less stable. The Turiasauria might represent a distinct group of non-neosauropods with a wide geographic distribution across Europe and Africa during the Late Jurassic.