A New Sciuravid Rodent (Mammalia) from the Early Eocene (Bridgerian) and the Sciuravid-Eomyid Transition

ABSTRACT A new genus and species of sciuravid rodent, Perasciuravus mcintoshi, is named from the late Bridgerian (early Eocene) of the Washakie Formation, southcentral Wyoming. The most distinguishing characters of the species (and genus) are that it retains the primitive condition of the zygomasseteric structure for rodents, characteristic of sciuravids, but has a more specialized dental morphology of the cheek teeth (complete ectolophids and hypolophids on the lower molars; complete metalophs and protolophs on the upper molars) typical of the later-occurring family of geomyoid rodents, the Eomyidae. Perasciuravus is viewed as morphologically transitional between the Sciuravidae and the Eomyidae. Its occurrence also overlaps the temporal range of the Sciuravidae (Wasatchian [early Eocene] to Duchesnean [early-late Eocene]) and predates the first occurrence of the Eomyidae (Uintan [middle Eocene]).