Revisiting Velocisaurus unicus Bonaparte 1991 (Theropoda, Ceratosauria, Noasauridae): inferences on the Noasauridae/Abelisauridae systematic

Abstract

In 1991, Bonaparte described Velocisaurus unicus upon an almost complete right tibia and a near complete right autopodium. He regarded this specimen a new taxon on the base of a metatarsal II and IV very mediolaterally compressed, being the metatarsal III two to three times wider than metatarsals II and IV. Brusatte and Carrano considered this taxon devoid of peculiar characters, although they kept it valid on the base of its provenance. In contrast, Brisson and colleagues reported a new specimen of this species and reinforced its validity by identifying three new autapomorphies. Indeed, all Velocisaurus’s autapomorphies cited by the aforementioned authors seem to have a rather wide distribution within Noasauridae, or even they are convergent with Abelisauridae. For instance, a triangular transverse section of the proximal end of the femur (hypertrophy of anterior muscular line) is present also in the abelisaurids Ekrixinatosaurus, Xenotarsosaurus, Skorpiovenator and Aucasaurus; the presence of transversely thin metatarsals II and IV are typical of noasaurids, however, the rod-like shape of metatarsals II mentioned by Brisson and colleagues is based on a fragmentary and weathered specimen; a phalanx IV-1 with a triangular proximal surface, and a dorsal facet narrower than the ventral one with a medial tilting is present also in Vespersaurus, Skorpiovenator and Aucasaurus. Although we regard Velocisaurus unicus as representative of a likely valid taxon, the discovery of additional specimens with new anatomical data will be essential for the taxonomy of this form.