The anatomy, phylogenetic relationships, and stratigraphic position of the Tithonian–Berriasian Spanish sauropod dinosaur <italic>Aragosaurus ischiaticus</italic>

Abstract

The first dinosaur to be named from Spain, the sauropod Aragosaurus ischiaticus Sanz, Buscalioni, Casanovas and Santafé 1987, is known from associated postcranial remains of one individual from the Las Zabacheras site in Galve, Teruel Province, Spain. Results of recent fieldwork confirm that the Las Zabacheras site represents a deltaic sediment complex in the Villar del Arzobispo Formation with a Tithonian–Berriasian (latest Jurassic–earliest Cretaceous) age. Description of the anatomy of Aragosaurus (including several previously undescribed elements) enables a re-evaluation of this taxon's relationships. Aragosaurus ischiaticus has six autapomorphies in the axial and appendicular skeleton, including the presence of epipophysis-like protuberances on middle caudal postzygapophyses. Phylogenetic analyses, using three independent data sets, support the view that Aragosaurus is a basal macronarian sauropod, lying outside of Titanosauriformes. Aragosaurus possesses derived states that are shared with basal Titanosauriformes, indicating that some characters previously considered to represent titanosauriform synapomorphies have a slightly wider distribution. A tooth, previously described as Aragosaurus, cannot be referred to this taxon as it was recovered from a different locality, and there are no overlapping elements with the holotype; it is here regarded as representing an indeterminate titanosauriform. These results, combined with new data on the stratigraphic age of Aragosaurus, demonstrate that basal macronarian sauropods were present in Europe at the end of the Late Jurassic, alongside more derived titanosauriforms. Aragosaurus is one of four genera of sauropod recovered from the Villar del Arzobispo Formation in Spain, making the latter an important contributor to our understanding of Late Jurassic sauropod diversity alongside the well-known contemporaneous faunas of the African Tendaguru Formation and the North American Morrison Formation. © 2014 The Linnean Society of London