New Mexico Geological Society Annual Spring Meeting — Abstracts

Near Cabezon in west-central Sandoval County, New Mexico, lenses of the coarse-grained sandstones of the Upper Cretaceous (Coniacian) Tocito Sandstone produce abundant quantities of selachian teeth and other fossils. The vast majority, picked from sieved anthills, are 5 mm or less in size, with a few larger fossils found adjacent to the anthills. The Tocito Sandstone is sandwiched between a lower tongue of the Mulatto Member of the Mancos Shale and an upper tongue of the Mulatto, and the inoceramid bivalves in the Mulatto both above and below the Tocito near Cabezon indicate an early Coniacian age. The Tocito has been interpreted as offshore sands deposited parallel to the coastline of the Western Interior Seaway. The most common of the Tocito selachians are from the order Lamniformes, representing the two families Odontaspididae (Cretolamna appendiculata) and Mitsukurinidae (Scapanorhynchus sp.). Other taxa present include Hybodus sp., Polyacrodus sp., Ptychodus mortoni, Squalicorax sp., cf. Scindocorax sp., Cantoscyllium sp., Ptychotrygon sp., Texatrygon sp. (possible new species), as well as other selachians yet to be identified. Non-selachian fish include cf. Micropycnodon kansasensis, cf. Coelodus stantoni, and at least one other teleost. One gar (represented by a single scale) that apparently washed down from a freshwater source, has been identified. In addition to the fishes, reptiles (crocodilians), cephalopods (ammonoids), inoceramid clams and various gastropods have also been documented. This assemblage has both increased the Coniacian vertebrate taxa known from New Mexico and extended the ranges (stratigraphic and geographic) of some of these species.