FOSSIL FISHES FROM THE LOWERMOST GREENHORN LIMESTONE (UPPER CRETACEOUS: MIDDLE CENOMANIAN) IN SOUTHEASTERN COLORADO

The Comanche National Grassland in southeastern Colorado is managed by the USDA Forest Service. The grassland includes exposures of the Lincoln Limestone Member of the Greenhorn Limestone (Upper Cretaceous: Middle Cenomanian; ca. 95 Ma). The lowermost portion of this stratigraphic member contains calcarenite beds, that are rich in disarticulated remains of marine vertebrates. Both surface collecting and acid treatment of rocks have yielded a variety of elasmobranch and teleost fossils. The identified elasmobranch taxa include: Ptychodus cf. P. anonymus Williston, Ptychodus decurrens Agassiz, Ptychodus occidentalis Leidy, Carcharias saskatchewanensis (Case, Tokaryk, and Baird), Carcharias tenuiplicatus (Cappetta and Case), Cretolamna appendiculata (Agassiz), Cretodus semiplicatus (Munster in Agassiz), Cretoxyrhina mantelli (Agassiz), Squalicorax curvatus (Williston), Squalicorax falcatus (Agassiz), Rhinobatos incertus Cappetta, and Cretomanta canadensis Case, Tokaryk, and Baird. The occurrence of these elasmobranch taxa is consistent with other Middle Cenomanian elasmobranch faunas of the North American Western Interior Sea. Among these taxa, teeth of Ptychodus, Cretoxyrhina, and Squalicorax are the most common elasmobranch fossils at this locality. The identified teleost taxa include Xiphactinus audax Leidy, Protosphyraena sp., and Enchodus sp. Teeth of Enchodus are the most common vertebrate fossils at this locality.