NEW LATE CRETACEOUS (EARLY CAMPANIAN) MICROFOSSIL ASSEMBLAGE FROM THE UPPER CRETACEOUS OF NEW MEXICO

The marine and marginal marine deposits of the Cretaceous western interior seaway in New Mexico locally preserve abundant fossil vertebrates. In this poster we compare fossils from an exceptionally rich early Campanian locality (NMMNH L-5636) to both older marine assemblages and nonmarine assemblages of the younger Fruitland and Kirtland formations. Most of the fossils were found in a poorly-sorted, polymictic intraformational clay-pebble conglomerate lag that is locally bone-bearing and were collected by screenwashing. Thousands of identifiable fossils were recovered, of which about 85% of fossils are fish (Chondrichthyes and Osteichthyes), with the remaining 15% representing tetrapods, including amphibians, turtles, crocodilians, Ornithischia, Theropoda, and mammals. The chondrichthyan taxa we report include the rhinobatid Cristomylus, the hybodont Lonchidion, the odontaspidid Carcharias, the mitsukurinid Scapanorhynchus, and the cretoxyrhinid Cretodus. Osteichthyan taxa include the phyllodontid Paralbula, the amiid Melvius, and indeterminate lepososteid and pycnodontid teeth. Lissamphibians are represented by a dentary fragment of an albanerpetontid-like batrachian. Most of the turtle fossils are unidentifiable shell fragments, but trionichid shell fragments are common in this stratigraphic interval. Identifiable crocodilians include teeth of alligatoroids represented by a Leidysuchus-like ziphodont morph and a durophagous Brachychampsa-like morph. Dinosaur fossils recovered include teeth of an indeterminate hadrosaurid and tyrannosaurid, as well as the dromaeosaur Saurornitholestes. The geology of the locality physically resembles the Menefee Formation, although recent geologic maps depict the site as lying within the overlying Lewis Shale. The fossiliferous horizon is primarily composed of crossbedded sandstone (lithic wacke) with bentonitic mudstone interbeds, as well as some strata containing lignite or siderite nodules, which suggest fluvio-deltaic environments. However, many of the recovered taxa, including most sharks and some osteichthyans, point to significant marine influence. At the same horizon nearby is a log riddled with Teredolites (“shipworm burrows”), further supporting our inference of marine influence.