The first Eocene vertebrate assemblage known from the Great Basin, the Elderberry Canyon Local Fauna, occurs in rocks referred to the Sheep Pass Formation near Ely, Nevada. Approximately 40 taxa are now known, including small anuran amphibians, small reptiles, birds, and mammals. The mammalian component consists of: the insectivorans Apatemys bellus, Pantolestes longicaudus, a tiny apternodont, at least one nyctitheriid, and at least four other taxa representing dormaalid and/or erinaceid erinaceomorphs; an epoicotheriid palaeanodont, cf. Tetrapassalus mckennai; the primates Notharctus tenebrosus, Trogolemur myodes, and two species of uintasoricines; the rodents Reithroparamys delicatissimus, R. cf. R. huerfanensis, Sciuravus sp., Microparamys sp., Pauromys sp., Mattimys sp., and two new genera; the hyaenodont Sinopa minor; two viverravid carnivores including Viverravus; the condylarth Hyopsodus paulus; the perissodactyls Hyrachyus modestus, Hyrachyus affinis, Helaletes nanus, Isectolophus latidens, and a new genus and species; and the artiodactyl Antiacodon pygmaeus. Greatest faunal similarity is with the Black’s Fork Member (or lower), Bridger Formation, and other early Bridgerian localities such as Powder Wash in the Douglas Creek Member of the Green River Formation in northeastern Utah. The age of the Elderberry Canyon Local Fauna can confidently be called early Bridgerian. The Elderberry Canyon Fauna is preserved in carbonate rocks believed to have been deposited in a shallow, warm, heavily vegetated, permanent, hardwater lake. The mammals lived on marshy wetland terrain adjacent to the lake, although some faunal elements may have been transported in from more distant habitats.

Two new genera and species of plagiomenids (Mammalia, ?Dermoptera, Plagiomenidae) are described from the North American Uintan (middle Eocene) and Chadronian (early Oligocene). A third genus and species, Ekgmowechashala philotau, from the early and middle Arikareean (late Oligocene) of the northern United States, is removed from the primate family Omomyidae and placed in the Plagiomenidae. All three newly recognized plagiomenids are placed in the Ekgmowechashalinae, sister subfamily to the subfamily Plagiomeninae (new rank). Ekgmowechashaline plagiomenids are somewhat primate-like, as is the plagiomenine genus Worlandia, but the Plagiomenidae are usually considered to be allied to the living colugos of southeast Asia, order Dermoptera. Analysis of that relationship is placed outside the scope of this paper. Tarka stylifera, the earliest known ekgmowechashaline, occurs in the type section of the Tepee Trail Formation, early Uintan (Shoshonian: late medial Eocene) of northwestern Wyoming. This locality falls in paleomagnetic Chron C20R, interpreted to be close to 47.5 Ma in age. A second, more primitive but later-occurring ekgmowechashaline genus and species, Tarkadectes montanensis, is from a nominally early Oligocene level (Chadronian) in the Kishenehn Formation of northern Montana. Ekgmowechashala is known from lower dentitions from the early Arikareean Sharps Formation of South Dakota and probably from an upper dentition reported from middle Arikareean rocks in the John Day Formation of Oregon. Ekgmowechashala is placed with the other two genera because of lower cheek-tooth morphology, but it lacks the enlarged incisor of Tarka. Ekgmowechashalines are hypothesized here to be primarily frugivores, folivores, and nectar- and exudate-feeders. Until now, known undoubted plagiomenids were restricted to the Paleocene and early Eocene (Wasatchian). The newly recognized post-Wasatchian occurrences are all in the northern part of the United States and are in keeping with previously known plagiomenid geographic distribution, which ranged from northern Wyoming to the Canadian arctic and possibly beyond.