A new titanosaur braincase from Neuquén Province, Northern Patagonia, Argentina.

CALVO, JORGE O.; GONZÁLEZ RIGA, BERNARDO J.

La Plata

Congreso; 20º Jornadas Argentinas de Paleontología de Vertebrados; 2004

Comisión Organizadora de las Jornadas Argentinas de Paleontología de Vertebrados

Most of titanosaurs are represented by incomplete skeletal elements lacking well-preserved cranial remains. In this context, the discovery of a braincase is relevant from systematic viewpoint. The fossil was found in March 1999, during the 60th paleontological expedition to Patagonia directed by J.O. Calvo. It comes from Loma del Lindero site, 8 km west to Rincón de los Sauces, and it was collected in fluvial facies tentatively assigned to the Río Neuquén Subgroup (late turonian-late Coniacian). It was found together with other titanosaurid bones that include procoelous caudal vertebrae and semilunar sternal plates. The braincase is slightly constructed and it preserves a fragment of the parietal and frontal, complete supraoccipital, the right paraoccipital process, basioccipital condyle, basal tuberas, a fragment of the basipterygoid process, and partially preserved orbitosphenoid, crista prootica and parasphenoid. It is characterized by: 1) the frontal participates on the anterior rim of the supratemporal fenestra, like in titanosaurids Rapetosaurus and Nemegtosaurus. In contrast, this character is absent in Saltasaurus and non-titanosaur sauropods (camarasaurids, diplodocids), 2) relatively reduced supraoccipital with a longitudinal groove in the sagital plane, like in Saltasaurus and Quaestitosaurus, 3) The paraoccipital, laterally directed, has a subquadrangular shape. It shows partially preserved process directed ventrally, such as is characteristic in titanosaurids Rapetosaurus, Nemegtosaurus and Saltasaurus, 4) Basal tubera are fused with the basipterygoid processes and, 5) basipterygoid processes are ventrally directed. The available fossil record of titanosaurs limits the definition of braincase unambiguous synapomorphies. However, the braincase described shares characters with typical titanosaur species and it can be assigned to Titanosauria clade. Funding comes from National University of Comahue (T-013 and T-021), Agencia Nacional de Promoción Científica y Tecnológica (PICT 07-08277), and Chevron-Texaco.