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

Abstract

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.

An abelisaurid humerus from the Upper Cretaceous of India

“…2a, e), but its contour and size are consistent with the conical internal tuberosity characteristic of abelisaurids rather than the more craniocaudally compressed tuberosity of more basal abelisauroids (e.g., MCF-PVPH 53; Novas et al 2006). As seen in caudal view (Figs.…”

“…3b, c). This condition differs from that seen in more basal abelisauroids such as Masiakasaurus (Carrano et al 2002) and MCF-PVPH 53 (Novas et al 2006), in which the humeral head is craniocaudally more compressed, resulting in a more elliptical contour in proximal aspect (Fig. 3d, e).…”

“…Chatterjee and Rudra (1996) originally attributed a right humerus from the Rahioli site to an abelisaurid. However, Carrano et al 2002); e, j, o, MCF-PVPH 53 (from Novas et al 2006). Not to scale the humerus in question (ISIR 434) is short, robust, and mediolaterally expanded at both ends, its proximal end lacking typical abelisaurid features such as a bulbuous head and a highly reduced deltopectoral crest.…”

“…This caudal tuberosity may constitute a synapomorphy of Abelisauroidea (Novas et al 2006), and probably served for the insertion of the M. latissimus dorsi and part of the M. deltoideus (Jasinoski et al 2006;Carrano 2007).…”

Aniksosaurus darwini gen. et sp. nov., a new coelurosaurian theropod from the Early Late Cretaceous of Central Patagonia, Argentina

“…The distal end of the humerus is cranially bowed; on its cranial surface there are traces of an intercondylar depression. The hu- merus of Aniksosaurus is clearly distinguishable from these of abelisauroid theropods (e.g., Masiakasaurus, Carnotaurus, Aucasaurus), in which the dectopectoral crest is poorly developed and the humeral shaft is straight in both cranial and lateral views (Novas et al, 2006).…”