New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Cretaceous (Santonian-Campanian) Menefee Formation is by far the most extensively exposed nonmarine Upper Cretaceous lithostratigraphic unit in New Mexico. However, the Campanian-Maastrichtian Fruitland/Kirtland formations are more fossiliferous, and these units yield the vast majority of Upper Cretaceous tetrapod fossils known from New Mexico. Even the Moreno Hill Formation in western New Mexico, a partial stratigraphic equivalent of the Menefee, yields a more diverse fauna than the Menefee. We report here several new fossils from the Menefee Formation in the southeastern corner of the San Juan Basin. The Cleary Coal Member yields a vertebrate fauna of indeterminate amiids, lepisosteids, trionychid and baenid turtles, hadrosaurs, ankylosaurs, and an indeterminate tyrannosaur. Most of these records are based on extremely fragmentary material that is not diagnostic below the family level. New vertebrate records from the Allison Member include a fin spine fragment of a hybodont shark, possibly Lissodus or Lonchidion, lepisosteid fish, the trionychid turtle Adocus, a pelomedusid turtle, and an indeterminate ornithopod. Additionally, we tentatively identify one of the known hadrosaurs from the Allison Member as a lambeosaurine, the first such record from the Menefee. The rest of the vertebrate fauna known from the Allison Member of the Menefee Formation includes the baenid Baena nodosa, indeterminate trionychids, the alligator Brachychampsa montana (=B. sealeyi) and other, indeterminate crocodilians, the centrosaurine informally known as the “Menefee ceratopsian,” indeterminate hadrosaurids, and the dromaeosaur Saurornitholestes sp. Another new record, from the Menefee Formation undivided, is of the solemydid turtle cf. Naomichelys. Presently vertebrate trace fossils from the Menefee Formation are limited to coprolites, which are relatively rare. Based on litho- and biostratigraphy, the Clearly Coal Member is probably late to latest Santonian in age, and the overlying Allison Member is of early Campanian age. Tetrapod faunas of late Santonian to early Campanian age are rare in western North America, so the Menefee Formation holds the potential to fill this important gap in the Upper Cretaceous tetrapod record.