A large sauropodiform (Dinosauria, Sauropodomorpha) from the Upper Triassic Quebrada del Barro Formation (Marayes-El Carrizal Basin), San Juan Province, Argentina

MARTINEZ, RICARDO NESTOR; APALDETTI, CECILIA; ABELÍN, DIEGO; GARCIA, GONZALO

General Roca

Congreso; XI Congreso de la Asociación Paleontológica Argentina; 2016

UNRN

Among the diverse vertebrate groups discovered at the Late Norian Quebrada del Barro Formation (QBF) of the continental Marayes?El Carrizal Basin (San Juan Province), one of the most abundant and diverse are the non-sauropod sauropodomorph dinosaurs. Here we present a new large sauropodomorph (PVSJ 1086 and 1087) exhibiting some anatomical features that resemble the basal Sauropoda condition (e.g., shortening manus, straightening forelimb). PVSJ-1086 consists in an almost complete articulated forelimb and a series of articulated posterior cervical vertebrae, whereas PVSJ-1087 includes some partial dorsal and caudal centra, and incomplete forelimb and hindlimb. Two autapomorphies difference the new specimen from all other basal Sauropodomorpha, including the recently known sauropodiform from QBF (PVSJ-908): proximal end of the ulna with a lateral margin 2 times larger than medial margin (radial fossa margin), and posterior cervical neural arches (from neurocentral suture to postzypapophyses level) more than 2 times higher than the posterior face of the centrum. Preliminary phylogenetic analysis depicts the new specimens in a polytomy with Lessemsaurus Bonaparte, 1999, and Antetonitrus Yates and Kitching, 2003, supported by one unambiguous synapomorphy: transverse width of distal humerus greater than 33% of its total length. This clade suggests that some Sauropodiformes have reached several sauropod-like features (e.g., elongation of neural arch) that allowed them to achieve noticeably larger body size already at the Late Norian, some million years before than the undoubtedly sauropods acquired giant forms. The new specimens add a new record to the diverse non-Eusauropod Sauropodiformes, group exclusively restricted to the Southern Pangea.