Sauropod (Dinosauria: Saurischia) remains from the Mercedes and Asencio formations (sensu Bossi, 1966), Upper Cretaceous of Uruguay

Several sauropod remains from Upper Cretaceous deposits of Uruguay are described herein. The Mercedes Formation (Campanian–Maastrichtian) in Florida department in central Uruguay, yielded abundant remains of small to middle-sized individuals. An ulna, five femora, a tibia and four caudal centra were recovered, all silicified, broken and showing different degrees of abrasion. The combination of several synapomorphies such as a lateral bulge in the femoral shaft, developed olecranon and strongly procoelous caudal centra, suggest that the remains belong to a lithostrotian sauropod. These are the first sauropod bones unequivocally yielded by the Mercedes Formation (sensu Bossi, 1966). The Asencio Formation (Maastrichtian?) in Río Negro department in western Uruguay yielded an isolated caudal vertebra. It is strongly procoelous and show additional characters (e.g. strongly inclined anterior margin, dorsally displaced apex of the condyle, posteriorly pointing transverse processes) which strongly suggest affinities to the Aeolosaurini. A phylogenetic analysis retrieved the Río Negro titanosaur in a clade along with the two Aeolosaurus species and Punatitan. The Campanian–Maastrichtian biochron of the tribe confirms a latest Cretaceous age for the Asencio Formation.