FIRST RECORDS OF TWO LARGE LAND MAMMALS IN MIDDLE EOCENE COASTAL PLAIN STRATA OF TEXAS

Two large land mammals are now recognized as belonging to the late middle Eocene Casa Blanca local fauna from Laredo, Texas. The Casa Blanca fossil community comes from an estuarine, Nypa-mangrove facies of the Laredo Formation. Analyses of new specimens has allowed refinement of more generalized identifications presented in earlier publications. It is now apparent that a previously undetermined mesonychid is Harpagolestes, cf. H. uintensis, and an unidentified brontothere is Notiotitanops mississippiensis. Harpagolestes is known from several Uintan North American Land Mammal Age (NALMA) faunas, with H. uintensis reported from Utah and Wyoming, H. cf. H. uintensis from the Candelaria local fauna of Trans-Pecos, Texas; Harpagolestes sp. from the Swift Current Creek local fauna of Saskatchewan, and cf. Harpagolestes sp. from the Friars Formation of southern California. The holotype locality and previous sole record of the bronothere Notiotitanops mississippiensis is an outcropping of the late middle Eocene Cook Mountain Formation exposed near Quitman, Mississippi. The Casa Blanca community is unusual in that it is comprised of specimens of land mammals, tropical rain forest and mangrove macro- and micro-flora; estuarine and marine invertebrates; terrestrial, arboreal and aquatic lower vertebrates, and a few bird skeletal elements. The presence of mammalian remains in North American Paleogene Coastal Plain deposits is extremely rare. The Casa Blanca mammals include 31 species. Although nine of the species are endemic to the Laredo area, the community correlates best with the Uinta C fauna from the Uinta Basin of Utah and its Uinta C correlates in Trans-Pecos, Texas and southern California. Correlations using marine invertebrates such as Turritella cortezi indicate the Laredo Formation is a parallic extension of the open marine Hurricane Lentil of the Cook Mountain Formation of east Texas, Louisiana and Mississippi. The Cook Mountain Formation bears NP16 nannoplankton and P13 planktonic forams which allow correlation with the early Bartonian strata of Great Britain and Europe.