Approximately 15 tons of screen-washed marginal marine sediments from the middle Eocene Laredo Formation, Claiborne Group, of Webb County, Texas have yielded the remains of the most diverse vertebrate biota known from Eocene deposits of the North American Coastal Plain. Thirty mammalian species are associated with three birds, 11 reptiles, an amphibian, 15 chondrichthyan and osteichthyan fishes, and nine species of terrestrial plants. Paleoecological analyses of vertebrate, invertebrate, and micro- and macrofloral remains indicate that the community lived in or near a tropical, Nypa mangrove-estuarine complex. The mammalian fauna indicates that the middle section of the Laredo Formation is correlatable with Uinta C (North American Land Mammal Age) faunas throughout the western interior of North America.