The oldest titanosaur sauropod dinosaur: a new specimen from the lowermost Cretaceous of Patagonia

GALLINA, P. A.; CANALE, J. I.; CARBALLIDO J. L.

Jornada; Jornadas Argentinas de Paleontología de Vertebrados; 2019

Titanosaurs are the best represented group of sauropod dinosaurs in Patagonia, recorded from Albian (upper Early Cretaceous) to Maastrichtian (upper Late Cretaceous) times. In fact, the Patagonian titanosaur record is the richest of the group worldwide. In recent fieldworks, incomplete cervical, dorsal and caudal vertebrae, a fragmentary distal femur, a fibula, and a scapula of a new titanosaur sauropod (MMCh-Pv228) were recovered from the Berriasian-Valanginian Bajada Colorada Formation, Neuquén province, Argentina. Both cervical and dorsal centra are camellate, a synapomorphy of titanosauriforms. The anterior caudal centrum is massive, slightly procoelus (a synapomorphy of Titanosauria) and bears a deep pneumatic fossa laterally, an uncommon character-state among somphospondylans. The scapular blade is distally expanded, the acromial region is rounded and a single ventral triangular process is present, the latter is a widespread character amongst titanosauriforms. To test the phylogenetic position of the new sauropod we performed a cladistic analysis (91 taxa scored for 418 characters) in which MMCh-Pv228 was recovered as a titanosaur sauropod, showing different positions within this clade. The camellate presacral vertebrae and the ventral triangular process of the scapula indicate titanosauriform affinities, and the procoelous anterior caudal places the new specimen within Titanosauria. The presence of a basal titanosaurian sauropod in the lowermost Cretaceous of Patagonia suggests that the group was already stablished in the Southern Hemisphere during this time and reinforce the idea of a Gondwanan origin for the group, in contrast to those that suggested the titanosaurian origin in East Asia.