Fossil Marine Vertebrates from the Juana Lopez Member of the Upper Cretaceous Carlile Shale in Southeastern Colorado, USA

Abstract

The Juana Lopez Member of the Carlile Shale is a calcarenite rock that became deposited within the Western Interior Seaway of North America during the Late Cretaceous approximately 90 million years ago (early late Turonian). In this study, rock samples collected from a Juana Lopez Member locality in southeastern Colorado, USA, were dissolved with a weak acid to examine the taxonomic composition of vertebrate fossils. Although almost all of the specimens are represented by isolated bones and teeth that are microscopic, the paleofauna was found to be taxonomically diverse. The vertebrate assemblage includes at least 14 chondrichthyans, 20 osteichthyans, and five tetrapods. Some noteworthy occurrences include teeth of Protolamna sp., a pliosaurid plesiosaur, and possible avians. Although teeth of Enchodus spp. are the most abundant vertebrate remains collected, our study clearly indicates the existence of a diverse vertebrate assemblage in a shallow marine environment in southeastern Colorado when the Juana Lopez Member was deposited.