A NEW MIOCENE BEAVER FROM THE EASTGATE FAUNA, CHURCHILL COUNTY, NEVADA

Since the late 1950's, fossil vertebrate remains have been collected from near the town of Eastgate in Churchill County, Nevada. Fossil remains were collected from within a volcanic tuff which occurs in the basalmost section of the Monarch Mill Formation. The Eastgate local fauna is an assemblage of fish, amphibians, reptiles, birds, and mammals. The mammalian fauna comprises 25 families and 60 species (18 insectivores, one chiropteran, seven lagomorphs, 33 rodents, five carnivores, three artiodactyls, and three perissodactyls). This includes a new species of insectivore, two new genera of rodents, and several new species of rodents. The age of the fauna is not well defined but is either late Hemingfordian or early Barstovian.

The fossil mammals of the Eastgate fauna have been collected from 21 sites within the Monarch Mill Formation. Of the 21 fossil localities, three produced beaver remains of the genus Monosaulax (Rodentia: Castoridae). The beaver at Eastgate is evidenced by numerous mandibles with teeth, maxillae with teeth, edentulous mandibles and maxillae, and isolated teeth. These elements represent a range of life stages from juvenile to adult. They are sufficient to confirm a new species of Monosaulax, and the sample size is large enough for studies of morphological variation within the species.