The first record of Onchosaurus (dagger Sclerorhynchidae) from the Late Cretaceous of northern Mexico

The fossil record of sclerorhynchid elasmobranchs in Mexico has been relatively scarce. In this paper we report a partial rostral tooth assigned to the cosmopolitan genus Onchosaurus (dagger Sclerorhynchidae), originally preserved in a shell-bed matrix, collected at the Potrero del Llano locality, municipality of Aldama, Chihuahua, Mexico. The specimen most likely came from the Upper Cretaceous San Carlos Formation. The tooth has morpho-anatomical features that allow its attribution to the species Onchosaurus of. O. pharao, which has been previously described from localities in Egypt, Niger, DR of Congo, Angola, Syria, Japan, U.S.A., Brazil, Colombia and Peru. The rostral tooth represents the first record of Onchosaurus in Mexico and the fourth in North America, thus expanding its paleobiogeographic distribution.