BASAL TITANOSAURIAN SAUROPOD MATERIAL FROM THE MIDDLE CRETACEOUS GALULA FORMATION, RUKWA RIFT BASIN, SOUTHWESTERN TANZANIA

Sauropods were one of the most successful dinosaur clades with notable peaks in diversity in the Late Jurassic and Late Cretaceous. Titanosaurians represent the most speciose and diverse clade of Cretaceous sauropods, reaching a global distribution by the end of the Cretaceous. Despite this widespread occurrence, titanosaurians are rare components of Cretaceous African faunas. Two representatives are currently recognized, Malawisaurus from the Lower Cretaceous Dinosaur Beds (DB) of Malawi and Paralititan from Upper Cretaceous deposits near Bahariya Oasis, Egypt. Recent expeditions to the middle Cretaceous Galula Formation of the Rukwa Rift Basin (RRB) in southwest Tanzania have aided in expanding our knowledge into the Cretaceous titanosaurian diversity of Africa. Critical titanosaurian fossils recovered include a semi-articulated individual (RRBP 07409), isolated yet morphologically variable teeth, and several isolated, well-preserved limb elements (e.g., humeri) that express morphology consistent with titanosauriformes. Recovered elements of RRBP 07409 include components of the postcranial axial (cervical and caudal vertebrae, ribs) and appendicular (scapula, humerus, ulna, ilium, and pubis) skeletons. Both parsimony and bayesian phylogenetic analyses were conducted to assess the relationship of RRBP 07409 and is placed as the sister taxon to the clade consisting of Malawisaurus and ‘derived’ titanosaurians. RRBP 07409 differs from Malawisaurus in gross morphology of the caudal vertebrae and more robust humerus. Additionally, tooth morphotypes vary with regard to combinations of cross-sectional shape (cylindrical, elliptical, or D-shaped), slenderness (wide or thin), and number of wear facets (unworn, one, two, or three). At present, there are several slender teeth with high angled wear facets that is consistent with titanosaurians. However, other morphotypes are not readily assignable to any specific clade and need further comparative work. Ongoing comparative work on materials collected from the RRB and the DB of Malawi is necessary for differentiating these potentially contemporaneous faunas. A detailed survey and characterization of these assemblages is essential for developing paleobiogeographic comparisons with other sub-equatorial Cretaceous faunas.