New dinosaur remains increase theropod diversity in the Cañadón Asfalto Formation (Lower Jurassic), Chubut Province, Argentina

Abstract

The Jurassic record of South American theropods is scarce, being represented by only seven nominal species. Four of these species (Eoabelisaurus mefi, Asfaltovenator vialidadi, Condorraptor currumili and Piatnitzkysaurus floresi) have been found in Toarcian-aged localities in the Cañadón Asfalto Formation (Chubut Province, Argentina) and, as a result, this unit has the highest known diversity of Jurassic theropods on the continent. A dentary with teeth in situ (MPEF-PV 6775) was found close to the base of this formation and differs from the other species from the unit with overlapping morphology. MPEF-PV 6775 resembles the dentary of the Late Jurassic North American theropod Ceratosaurus in being a robust bone, with a strong dorsal curvature in lateral view, and having relatively tall tooth crowns. MPEF-PV 6775 was scored in two matrices that have a broad taxonomic sample focused on Theropoda and the new specimen was recovered in large polytomies with other early neotheropods. A third analysis was conducted scoring MPEF-PV 6775 into a matrix focused in ceratosaurs because of its morphological similarities to Ceratosaurus. In this analysis, MPEF-PV 6775 was recovered as the sister taxon to Ceratosaurus, sharing with the later a ventral margin of the dentary that is strongly convex anteroposteriorly. These results suggest that MPEF-PV 6775 is a ceratosaurian and probably a ceratosaurid. Thus, our results indicate a higher taxonomic diversity of theropods and, in particular, ceratosaurs in the Cañadón Asfalto Formation. MPEF-PV 6775 seems to provide more evidence for the presence of ceratosaurids in the Jurassic of South America, together with isolated teeth described from the Late Jurassic of Uruguay and some analyses that recovered Eoabelisaurus and Berberosaurus within this clade.