New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Cretaceous (upper Santonian -middle Campanian) Menefee Fonnation has a poorly known vertebrate record consisting of indeterminate hadrosaur, "carnosaur," ankylosaur, trionychid and baenid turtle, crocodylia, and amiid fish. New discoveries of vertebrate fossils from New Mexico Museum ofNatural History localities L-3033 and L-3034 from the Allison Member, Menefee Formation (lower Campanian) of the southeastern San Juan Basin furnish important additions to this fauna. New vertebrate fossils include a partial skeleton of a pachyrhinosaurine ceratopsian, a tooth of a dromaeosaurid theropod (cf. Sauromithoides), a partial skull and associated lower jaws of the alligatorid crocodilian Brachychampsa, carapace fragments oftrionychid turtles, and carapace and plastron fragments of baenid turtles.

The ceratopsian partial skeleton includes parts ofthe skull and mandible, several vertebrae, several ribs, a partial ilium, and a femur. The skull and mandible elements include a nearly complete left squamosal, a left dentary and a complete predentary. This is among the oldest ceratopsians from North America and the first occurrence of a pachyrhinosaurine ceratopsian from the southern Rocky Mountain region. The new specimen ofthe rare alligatorid Brachychampsa is a new species and represents the fourth and oldest reported skull ofa Cretaceous alligatorid.

North American terrestrial vertebrate faunas of early Campanian age are generally poorly known. Results ofa preliminary investigation ofthe vertebrate paleontology of the Allison Member, Menefee Formation suggest that it may yield a significant vertebrate fauna of early Campanian age.