Cranial osteology of Bajadasaurus pronuspinax (Sauropoda, Dicraeosauridae)

The cranial remains of the holotype of the Lower Cretaceous Bajada Colorada Formation (Neuquén, Argentina) Bajadasaurus pronuspinax and its associated 3D model are studied and compared herein. These materials comprise a complete braincase, skull roof and occiput, several periorbital elements, several palatal elements, a partially complete upper jaw and complete lower jaw, a partially complete functional dentition, and an indeterminate element. Three potential synapomorphies for the taxon, related to the temporomandibular articulation area, were recognised, two of them in the quadrate and one in the squamosal. Four potential synapomorphies for Dicraeosauridae were recognised, related to the braincase and the jaws, in the orbitosphenoids, prefrontals, maxillae and dentaries, and surangulars. The new information highlights the variability and similarities among Dicraeosauridae, allowing the reassessment of previously suggested skull configurations within the group, which are reinterpreted here a presenting stylised lower jaws, and suggests the presence of a cornified sheath on the rostral portions of the muzzle, such as the observed in other dinosaurian groups.