Biostratigraphic and paleoecologic implications of the first Eocene land mammal fauna from the North American coastal plain




Westgate, James W.

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A newly discovered vertebrate fossil assemblage, the Casa Blanca local fauna, comes from the Laredo Formation, Claiborne Group, of Webb County, Texas, and is the first reported Eocene land mammal fauna from the coastal plain of North America. The mammalian fauna is correlated with the Serendipity and Candelaria local faunas of west Texas, the Uinta C faunas of the Rocky Mountains, the Santiago Formation local fauna of southern California, and the Swift Current Creek local fauna of Saskatchewan. The vertebrate-bearing deposit lies approximately 32 m above a horizon containing the marine gastropod Turritella cortezi which ranges from east Texas to northeast Mexico in the lower half of the Cook Mountain and Laredo Formations and is a guide fossil to the Hurricane Lentil in the Cook Mountain Formation. Nannoplankton found in these middle Eocene formations belong to the upper half of Nannoplankton Zone 16 and allow correlation with European beds of upper Lutetian to lower Bartonian age. The Casa Blanca fauna includes eight chondrichthyan, six osteichthyan, one amphibian, 10 reptillian and one avian species. More than 600 specimens represent at least 30 species of 28 mammal genera. The Casa Blanca fauna is the southernmost and easternmost North American land mammal fauna of definite Eocene age, and is the westernmost Paleogene vertebrate fauna from the Gulf Coastal Plain. Four lower vertebrate species previously known from the Old World are reported from Eocene deposits of North America for the first time. Local paleoecologic conditions probably resembled those of the present day coastal areas of southern Mexico and northern Central America.