New Abelisauroidea (Theropoda, Ceratosauria) remains from Cerro Fortaleza (Cerro Fortaleza Formation), Santa Cruz Province, Argentina

CANALE, JUAN IGNACIO; PAULINA CARABAJAL, ARIANA; MÉNDEZ, ARIEL; LEE, YUONG NAM

Puerto Madryn

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2018

Abelisauroid theropods constitute the most commonly recorded meat-eating dinosaurs from the Upper Cretaceous of Gondwana. In Argentina, they are known mainly from central and northern Patagonia, especially Neuquina Basin. However, their record in the southern region of Patagonia is scarce, although the Cretaceous outcrops of the Magallanes Basin are extensive. In this contribution we present new abelisauroid remains (MPM-PV 19111), consisting of two partial metatarsals, recovered from Cerro Fortaleza Fm (Campanian), Santa Cruz province. The metatarsal III (MPM-PV 19111-1) is represented by a distal articular end, which shows a rectangular contour in distal view, and wide and well-developed colateral pits. The proximal end of the metatarsal IV (MPM-PV 19111-2) shows a D-shaped articular surface; with a gently concave medial surface for the articulation with the metatarsal III, a sharp posteromedial margin, and a flat lateral margin which curves medially at its dorsal sector, giving a triangular cross-section to the diaphysis; a combination of features present in abelisauroids. Other putative abelisauroid recovered from the same formation is the enigmatic Austrocheirus isasii, which phylogenetic relationships are yet unclear. Although both, Austrocheirus and the new specimen preserved part of the metatarsal III, which show similar dimensions, there are no clear morphologic traits that could suggest that both could represent the same taxon. The new specimen adds to the knowledge of the dinosaur fauna of ?Cerro Fortaleza? Formation, supporting the presence of mid-sized abelisauroids in the Campanian of southern Patagonia, together with megaraptorid theropods, giant sauropod titanosaurs, and elasmarian ornithopods.