A large titanosaur sauropod from the Early Cretaceous of Patagonia, Argentina.

JOSÉ LUIS CARBALLIDO; ALEJANDRO OTERO; IGNACIO A. CERDA; LEONARDO SALGADO; DIEGO POL

Simposio; First Brazilian Dinosaur Simposium; 2013

Gigantic body size evolved independently in different sauropod lineages, being the Late Cretaceous Patagonian titanosaurs the clade in which the largest dinosaurs are registered (Argentinosaurus and Puertasaurus). Nevertheless the incompleteness of these giant taxa obscures the characterization of their relationships among basal titanosaurs and therefore precludes the fully understanding of the evolution of extreme gigantism within this clade. We present a new giant and well-preserved titanosaur specimen, recently discovered in a new locality of the Cerro Barcino Formation (Early Cretaceous; northern Patagonia), which represents the first definitive record of this group in the Early Cretaceous of Patagonia. A preliminary excavation of these remains reveled that this specimen contain enough elements to be considered the most complete within giant titanosaurs, being only comparable in body size to Argentinosaurus (or even slightly larger). The already exposed remains are semi-articulated and include: a femur, both pubes, both ischia, one ilium, a scapula, a humerus, an ulna, dorsal and caudal vertebrae, ribs, one chevron, and an isolated sauropod tooth. Additionally several not excavated bones were observed, which represents more axial and limb materials. Field observations allow a preliminary taxonomic characterization of the specimen, which can be recognized as a titanosauriform due to the presence of spongy presacral bony texture, dorsal ribs with pneumatic cavities, caudal centra with the neural arch set on anterior half of the centrum and a femoral lateral bulge. Besides, the recognition of anterior and anterior and middle caudal central with ventral longitudinal hollow place this specimen within Titanosauria. The importance of this new specimen relies on its completeness and well preservation which contrast with the average record of gigantic titanosaurs worldwide. Besides, whereas the already known taxa comes from Late Cretaceous, our new specimen is registered in the Early Cretaceous, demonstrating that extreme large body titanosaurs evolved before that previously thought.