Fossiliferous deposits of the Greenhorn Limestone (Upper Cretaceous) are found on the Comanche National Grassland in southeastern Colorado. The lowest portion of the Greenhorn Limestone, the base of the Lincoln Limestone Member, contains calcarenite beds rich in disarticulated remains of marine vertebrates. We examined the composition of the vertebrate paleofauna from one particular location (Tobe locality) through surface collecting and acid solution of rocks. The paleofauna is taxonomically diverse, consisting of 22 chondrichthyans, at least 15 osteichthyan fishes, and six aquatic reptiles. Molluscan taxa indicate that the basal Lincoln Limestone in southeastern Colorado was deposited sometime between middle Middle Cenomanian (ca. 95 Ma) and late Middle Cenomanian (ca. 94.7 Ma), and the composition of the vertebrate fauna (primarily chondrichthyan taxa) agrees with this interpretation. The Tobe locality was situated far from the shorelines of the Western Interior Seaway, with relatively high-energy waves impinging upon the seafloor, concentrating biogenic remains. Fossil remains within the calcarenite appear to have undergone minor time-averaging, based upon erosional rounding and breakage present in numerous specimens. Nevertheless, the deposit contains one of the best representative Middle Cenomanian vertebrate communities so far described from the Western Interior Seaway of North America. Considering that the paleofauna consists of taxa diverse in size, morphology, and inferred ecology, the trophic structure of the paleocommunity was probably complex.
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