A new arvicoline species (Rodentia: Crocetidae) from the Pliocene Panaca Formation, southeast Nevada

Abstract

Arvicoline rodents show a number of evolutionary trends in their dental morphology and provide a useful basis for biochronologic study in late Tertiary deposits. This paper describes a large dental sample of Mimomys from a site in the Panaca Formation, southeast Nevada. This sample provides the basis for naming of a new species, M. panacaensis. The new species is comparable in evolutionary stage to the two early Blancan species M. (Ophiomys) mcknighti and M. (Ogmodontomys) sawrockensis in its low dentine tract on the labial side of m 1, but it is differentiated from M. (Ophiomys) mcknighti in having some M3s with an enamel islet and/or three roots, and from M. (Ogmodontomys) sawrockensis in smaller size, higher percentage of the enamel islet on the ml, and the presence of two-rooted M3s. Compared to the middle Blancan species of Mimomys, M. panacaensis has more primitive characters, including smaller size, lower dentine tract on the labial side of ml, and/or a higher percentage of three-rooted M3s. M. panacaensis is considered early Blancan in age. The phylogenetic analysis of the North American early Mimomys places M. panacaensis as the sister-group of M. (Ophiomys) mcknighti + (M. (Ophiomys) magilli + M. (Cosomys) primus).