Fossil vertebrates from the Cerro del Pueblo Formation, Coahuila, Mexico, and the distribution of Late Campanian (Cretaceous) terrestrial vertebrate faunas

The Cerro del Pueblo Formation, Coahuila, Mexico, includes the southernmost Upper Cretaceous non-marine vertebrate assemblage in North America. Previously, the only well-documented vertebrates were dinosaurs, mainly ornithopods, and turtles. Recent work on the Cerro del Pueblo Formation has resulted in the recovery of a good sample of small tetrapods from different microvertebrate localities in the upper part of this Late Cretaceous unit of north of Mexico. Material from these sites augments the faunal list from the Cerro del Pueblo Formation. New amphibian taxa here described include the first occurrences of frogs and salamanders. Newly recovered reptiles represent five families of lizards; Anguidae, Teiidae, Necrosauridae, Varanidae, and Helodermatidae; two species of aniliid snakes (one of them new); a new genus and species of marine turtle from the tribe Bothremydini; the brevirostrine crocodile Brachichampsa; and the most southerly occurrence of a long snouted crocodile. New dinosaurs reported here include a ceratopsian and members of five theropod families: two dromaeosaurids including an indeterminate genus and the velociraptorine Saurornitholestes, the small theropods Troodon and Richardoestesia, an ornithomimid, and a large tyrannosaurid. The ornithomimid is represented by a partial skeleton and a new genus and species, Saltillomimus rapidus, is erected on the basis of this material. Mammals are represented by two kinds of marsupials, Turgidodon cf. T. russelli, and Pediomys cf. P. elegans, and generically indeterminate multituberculates of the families Taeniolabidoidae and Cimolomydae.;The fauna of the Cerro del Pueblo Formation is compared with the fauna from contemporaneous formations from further north, particularly the Aguja and Javelina formations of Texas, to give a more regional overview of the faunas of the southern portion of North America during the Late Cretaceous. The differences are shown in the diversity and number plants associated to new taxa of hadrosaurs and ceratopsians and the absence of sauropods in the Cerro del Pueblo Formation. Differences in the faunal composition of the Cerro del Pueblo and Aguja formations indicate that paleocological complexity was present in southern regions of North America during the Late Campanian. Thus together these formations can be considered to characterize the southern-most region of North America.