Cosomys, a New Genus of Vole from the Pliocene of California

Abstract

Rodents are of rather common occurrence in the later Tertiary of North America, yet voles have been completely absent from the record with the exception of a single tooth of Neofiber found in the upper Pliocene San Pedro Valley beds of Arizona. Consequently material representing this important group should prove of interest in an interpretation of the history of the voles in North America. The specimens described in this paper are from late Cenozoic mammal-bearing beds exposed on the flanks of the Coso Mountains along the eastern margin of Owens Valley, nine and one-half miles east of Olancha, California. The age of the deposits from which the rodent material comes has been tentatively regarded as upper Pliocene by Dr. Chester Stock of the California Institute of Technology. A determination of age has been afforded chiefly by horse material from the same locality. The author wishes to thank Dr. Stock for the opportunity to study the material and for advice during the course of the investigation. Specimens of Recent voles were loaned for comparison by Mr. Donald R. Dickey of the California Institute of Technology, and by the United States National Museum. Preparation of the illustrations was super- vised by Mr. John L. Ridgway.