New material and two new species of the poorly known rodent Rudiomys (Aplodontiidae: Meniscomyinae) from the late Oligocene John Day Formation of Oregon and the Renova Formation of Montana

Abstract Aplodontiid rodents are a diverse group of Oligo-Miocene rodents in North America that declined dramatically in the late Miocene leading to their current depauperate diversity of a single living species. The late Oligocene is a period of particularly high diversity for the group, especially in the northwestern quadrant of North America, including the Northern Great Plains, Northern Rockies, and Pacific Northwest regions. One of the more poorly-known genera in this time period is Rudiomys Rensberger, 1983, described from a single specimen that he designated the type of Rudiomys mcgrewi Rensberger, 1983, a fossil collected in the otherwise abundant vertebrate assemblages of the John Day Formation. Since that first publication, additional material of the genus has come to light, both in the type area in Oregon and in similarly aged deposits of western Montana’s Cabbage Patch beds. The new material from Oregon provides a more complete understanding of the dental morphology of the genotypic species. The Montana occurrences yield two additional species of the genus, Rudiomys drummondensis new species and Rudiomys intsook new species, which bear out some tentative ecological inferences from Rensberger’s original description, showing that Rudiomys is very likely a habitat specialist. This ecology explains its geographically limited distribution relative to other meniscomyine genera. The low-crowned dentition and bunodont morphology in this unusual aplodontiid could indicate a greater affinity for more closed habitats. This study not only yields a more complete understanding of the dental morphology of Rudiomys but also reveals the even greater diversity of late Oligocene aplodontiid species. UUID: http://zoobank.org/681f9549-ab2f-4ac1-ba87-9467a7609b34