New Mexico Geological Society Annual Spring Meeting — Abstracts

A new assemblage of Santonian selachians from the eastern side of the Rio Puerco was collected in the summer of 2009. This faunal assemblage was found in unconsolidated sand through both surface picking and screening, and is located in the lower Santonian Hosta Tongue, which is the lowest horizon of the Point Lookout Sandstone, which is the lowest of the stratigraphic units within the Mesa Verde Group. The sands were collected in various locations throughout an area of approximately one acre, and then screen-washed using a 1 mm mesh. This process yielded in excess of 200 teeth, representing at least four orders. Within these orders, at least 16 genera can be recognized, including three undescribed taxa that are new to the New Mexican selachian record. The teeth picked from the surface show much wear due to exposure, but the screenwashed teeth show little evidence of prior transport. Besides teeth, several dermal ossicles of selachians were also found, and teleost fossils, both teeth and vertebrae, were present in some abundance. This assemblage is dominated by lamniform species, especially those of Scapanorhynchus, Squalicorax, and Cretolamna. Rajiformes (Pseudohypolophus) and Pristiformes (Ischyrhiza) are also fairly common. Included in this assemblage are several shell fragments of soft-shell turtle (Trionychidae) and two pieces of very small reptile teeth. A listing of the selachian fauna would include three species of Squalicorax, as well as Cretolamna, Ptychotrygon, Cantioscyllium, Cretoxyrhina, Scapanorhynchus, Hybodontidae, Cretodus, Ptychodus, and Odontaspis.