New titanosaur remains from the Portezuelo Formation (Turonian-Coniancian) and their implications for the sauropod faunal diversity of the southern Neuquen Basin, Patagonia, Argentina

摘要

In the Neuquen Basin, the Portezuelo Formation (Turonian-Coniacian, Upper Cretaceous) is represented by extended fluvial outcrops that are well-known for yielding an abundant and diversified vertebrate fossil record. However, most of the sauropod fossil record is represented by incomplete specimens, and only two taxa are formally described for the upper Turonian-lower Santonian of the Neuquen Basin: Malarguesaurus and Futalognkosaurus. In this contribution we report new sauropod specimens composed of partially associated axial and appendicular elements coming from the upper section of the Portezuelo Formation of the Los Bastos locality, in the southern Neuquen Basin. The bones show a set of morphological features that allow us to refer them to a titanosaur sauropod: a "cone-chisel-like" tooth, procoelic caudal vertebrae, a dorsally expanded ulna olecranon, and a femur with a prominent lateral bulge and an elliptical diaphysis in cross-section. The phylogenetic analysis recovers the sauropod remains as an unstable colossosaurian within Titanosauria, an effect likely attributable to the incomplete condition of the specimens. Nevertheless, osteological and phylogenetic analyses, together with morphological comparisons with the sauropod fossil record of the Portezuelo Formation, suggest that the new specimens represent a titanosaur different to previously known taxa. Pending better preserved and more complete remains from Los Bastos, the new evidence allows us to improve our knowledge of sauropod diversity during the upper Turonian-lower Santonian, at least in the southern Neuquen Basin.