Turtles from the Late Cretaceous (Campanian) of El Gallo Formation, Baja California, Mexico

Turtles are typically important members of Late Cretaceous vertebrate assemblages throughout North America, and are considered a useful tool to define biogeographic patterns. In Mexico, Cretaceous turtles have been recorded in the states of Baja California, Chiapas, Chihuahua, Coahuila, Nuevo Leon, Puebla, and Sonora; specifically the state of Coahuila shows so far, the highest diversity of turtles. In this paper, the diversity of Late Cretaceous turtles from the El Gallo Formation (Baja California) is reviewed. Previously, only Naomichelys speciosa was recognized in this Formation. Based on fragments with distinctive sculpture patterns four additional taxa are recognized, Compsemys victa, Basilemys sp., Trionychidae indet., and cf. Chelydridae. With the recognition of these new taxa, the knowledge of Cretaceous turtles diversity of the El Gallo Formation is increased. This assemblage is unusual compared to other North American turtle assemblages because it suggests the presence of previously unrecognized biogeographic patterns. Here we report the first record of Basilemys sp. from the Late Cretaceous of Mexico and the presence of cf. Chelydridae on the western side of Laramidia.