Fossil mammals comprising the early (and perhaps earliest) Wasatchian Red Hot local fauna from the Gulf Coastal Plain of Mississippi are described. As currently understood, the fauna consists of 33 species of mammals, including the following new taxa: Mimoperadectes sowasheensis, new species; Apatemys pygmaeus, new species; Palaeosinopa aestuarium, new species; Naranius americanus, new species; Colpocherus mississippiensis, new genus and species; Diacocherus dockeryi, new species; Wyonycteris primitivus, new species; Choctawius foxi, new genus and species; Haplomylus meridionalis, new species; Ectocion nanabeensis, new species; Miacis igniculus, new species; Eogale parydros, new genus and species; Viverriscus omnivorus, new genus and species; Paramys dispar, new species; Corbarimys? nomadus, new species; and Franimys? actites, new species. New combinations proposed here include Plagioctenodon dormaalensis (Quinet, 1964), Plagioctenodon rosei (Gingerich, 1987), Choctawius mckennai (Szalay, 1969), and Paramys wutui (Tong and Dawson, 1995). The Red Hot local fauna derives from an estuarine sand unit that also yields fossil spores, pollen, dinoflagellate cysts, fishes, and snakes. The fauna is taphonomically biased against the preservation of mammals having medium to large body mass.

The Red Hot local fauna provides a rare opportunity to gauge the significance of biotic provincialism within North America near the Paleocene-Eocene boundary, a time of dynamic climate change. Faunal endemism with respect to the Rocky Mountain Interior of North America is high at the species level, consistent with evidence for substantive differences in the physical environment and flora. Several lines of evidence, including mammalian biostratigraphy, sequence stratigraphy, and dinoflagellate zonation, suggest that the Red Hot local fauna correlates with earliest Wasatchian (Wa-M) faunas from the Bighorn Basin of Wyoming. Latitudinal shifts in taxon ranges coincident with global warming provide an alternative explanation for seemingly transient episodes of phyletic dwarfing among mammals during the PETM in the Bighorn Basin.