An unexpected early record ofMictomys Vetus(Arvicolinae, Rodentia) from the Blancan (Pliocene) Glenns Ferry Formation, Hagerman Fossil Beds National Monument, Idaho

Abstract

The cooling during the Pliocene that preceded major continental glaciation in North America is recorded by thick fluvial and lacustrine sequences at Hagerman Fossil Beds National Monument (HAFO) in southcentral Idaho (McDonald et al., 1996). Fossiliferous beds at HAFO occur within the nearly 200 m of exposed Glenns Ferry Formation west of the Snake River. This formation extends from southwestern Idaho into easternmost Oregon (Malde and Powers, 1962). The Glenns Ferry Formation within HAFO contains hundreds of localities that are within the Blancan North American Land Mammal Age. Collection of specimens from these localities since the late 1920s has resulted in large repositories of fossils currently housed, in part, at the United States National Museum, the University of Michigan Museum of Paleontology (UMMP), and the Idaho Museum of Natural History (IMNH); additionally, smaller collections were accumulated by other museums (McDonald et al., 1996). Today the paleontological resources of HAFO are stewarded by the National Park Service. In spite of the extensive previous collections, significant new discoveries are still being made at HAFO.