New Mexico Geological Society Annual Spring Meeting — Abstracts

Last year, we discovered extremely rich microvertebrate locality early Campanian Allison Member of the Menefee Formation in northwestern New Mexico. This site has yielded a highly diverse paleofauna, including fish (Lepisosteidae and Amiidae) teeth, sharks (Lissodus, Cretodus, Carcharias, Cretolamna, Ischyrhiza, Onchosaurus, Squatina, and Squatirhina), rays (Ptychotrygon, Pseudohypolophus mcnultyi, Protoplatyrhina renae, Protoplatyrhina hopii, Dasyatis and Myledaphus), the earliest confirmed New Mexico mammals (Paracimexomys group of Eaton and Cifelli [2001]), maniraptoran (Richardoestesia isosceles) and dromaeosaurid (Saurornitholestes langtoni and S. sp.) theropod dinosaur teeth, hadrosaurid dinosaur teeth, Brachychampsa-like crocodilian teeth, lissamphibian teeth and jaw fragments referable to the salamander Albanerpeton, and squamate lizard scales. The aqueous fauna is by far the most abundant and diverse assemblage in the unit and provides information on the aqueous paleoecology of the Menefee Formation. Taphonomic study of the site indicates little or no transport of the fossils, and therefore little or no information addition, and thus this site yields is an accurate representation of the aqueous paleofauna of the Menefee. The taxa identified here are principally freshwater forms, and our analysis of the sedimentology of the source area confirms this hypothesis. There is enough information here to reconstruct a basic food web of the freshwater vertebrate fauna of the Menefee. This is done largely on the basis of tooth morphology and comparison with extant forms, as well as the use of ecological principles. We propose that dominant aqueous taxa in the Menefee were the chondrichthyans Pseudohypolophus, Ptychotrygon, Lissodus, and Onchosaurus. The dominance of these forms indicates an abundant invertebrate fauna of crustaceans and mollusks in the Menefee that was not preserved.