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.

A new genus, Paridiagonum, with the new species, Patidiagonum bidentatum, and a new species of Fortagonum Darlington, 1952, Fortagonum bellorum, are described from Mt. Misim in the vicinity of Wau, central eastern Papua New Guinea. The new genus in body shape is similar to the genus Idiagonum Darlington, 1952, but is distinguished from that genus by absence of setae at the prosternal intercoxal process, presence of three discal punctures on the elytra, bidentate apex of each elytron, deeply excised fourth tarsomeres, and much shorter and wider female gonocoxites 2, which lack the dorso-median ensiform seta. Structure of the fourth tarsomeres, however, suggests relationships with some species described by Darlington (1952) as belonging to Colpodes Macleay (e.g., Colpodes antedens Darlington, 1952, and Colpodes acuticauda Darlington, 1952). The new species of Fortagonum is distinguished from all described species by a combination of characters: chaetotaxy of head, pronotum, and elytra; distinctly fusiform shape of pronotum; rather triangular shape of the unarmed elytra; and structure of the aedeagus.

Two species of lagomorphs are represented in the Diamond O Ranch local fauna of southwestern Montana. Mytonolagus ashcrafti, new species, is the most common mammal at Diamond O Ranch, and is comparable in evolutionary grade to Mytonolagus wyomingensis Wood, 1949, and more advanced than either Mytonolagus petersoni Burke, 1934, or Mytonolagus near M. petersoni. A second species of lagomorph is represented by only a few specimens from near the base of the Diamond O Ranch section. The teeth of this form tentatively assigned to Palaeolagus Leidy, 1856, are significantly more hypsodont than those of M. ashcrafti. The Diamond O Ranch local fauna falls very near the Duchesnean—Chadronian boundary in one of the most poorly documented temporal intervals during the entire Cenozoic of North America.

Anuran fossils from the middle Miocene, early Barstovian Anceney Locality in Gallatin County, Montana, are described and identified as Scaphiopus neuter Kluge, 1966. The material consists of many isolated, complete to partial bones that represent most elements of the skeleton. Scaphiopus neuter was previously known by the holotype, a partial skeleton, from the late Oligocene, early Arikareean of South Dakota and a partial ilium from the Arikareean of Nebraska, and thus the new material increases the geologic age and geographic distribution of the species. Results from a phylogenetic analysis conducted to test the relationship of Sc. neuter to other pelobatids places it in a clade containing four extant species of Spea Cope, 1866. The new combination, Spea neuter (Kluge, 1966), is proposed for the oldest and only extinct member of this genus currently known. Within Spea, Sp. neuter is the sister taxon to the clade comprised of Spea intermontana (Cope, 1863) Spea bombifrons (Cope, 1863), a relationship supported by one synapomorphy: the septum nasi of the sphenethmoid forms a laterally expanded, vertical plate at its anterior end. Relationships of other members of Spea remain unresolved. A stratocladogram based on the pelobatid phylogeny presented here suggests an approximately 28 Ma ghost lineage for Spea.