Humerus of a basal abelisauroid theropod from the Late Cretaceous of Patagonia

Abstract

Here we describe a partial humerus of a medium-sized theropod dinosaur from the Upper Cretaceous (Late Turonian - Early Coniacian) Portezuelo Formation, Neuquén Province, Argentina. The humerus shares with Abelisauroidea and Elaphrosaurus an articular head proximally oriented, and deltopectoral crest strongly reduced. The bone is referred to Abelisauroidea on the basis of the following derived features: proximal tuberosity on caudal surface of humeral shaft, and greater tubercle at level with the medial tuberosity. The gracile morphology of the humerus, as well as the poor development of its medial tuberosity, resemble more Masiakasaurus than the condition present in abelisaurids (e.g., Carnotaurus, Aucasaurus), in which the humerus is more robust and the medial tuber-osity is prominent. Available information demonstrates that during deposition of the Portezuelo Formation large and bulky abelisaurids (e.g., Ekrixinatosaurus) lived together with gracile and medium-sized abelisauroids.