Osteology, relationship, and feeding ecology of the theropod dinosaur Noasaurus leali, from the Late Cretaceous of North-Western Argentina

Abstract

Noasaurus leali is a small (~2 m) carnivorous theropod and the nominal genus of the clade Noasauridae, one of the two radiations of abelisauroid ceratosaurs predominantly present in the Southern Hemisphere during the Mesozoic. This eponymous theropod from the Maastrichtian Lecho Formation of Salta, Argentina, is known from an incomplete skeleton of which the strongly curved manual ungual is the most peculiar element. We here provide for the first time a comprehensive description of the holotypic specimens of Noasaurus, whose phylogenetic position was explored using three independent datamatrices on theropod relationships. This species is diagnosed by several apomorphies such as a dorsal ridge in the maxillary fossa, a strongly arched quadrate, a cervical neural arch with anterior epipophyseal prongs, and a manual ungual with a subtriangular flexor fossa delimited by a V-shaped ridge. Results of the phylogenetic analyses recovered Noasaurus closely related to Velocisaurus, Masiakasaurus, and Laevisuchus, which together form a Late Cretaceous radiation of small-bodied noasaurids restricted to the Southern Hemisphere. The peculiar morphology of the lateral dentition and manual unguals suggests that Noasaurus was an opportunistic carnivore feeding on small prey items and a possible piscivore gaffing fish with its specialized hand claws.