Mammals from the Blue Ash Local Fauna (late Oligocene), South Dakota. Rodentia, Part 4: Family Aplodontidae

Ten species of aplodontid rodents are present in the Blue Ash local fauna, which currently represents the most diverse family of rodents in the assemblage. One new genus, Disallomys, is described with Allomys storeri Tedrow and Korth as the type species. Four new species are described, Disallomys robustus, D. intermedius, Prosciurus clausulus, and Niglarodon brachyodon. The aplodontids from the Blue Ash fauna suggest that it is more likely Whitneyan than Arikareean in age because of the abundance and diversity of prosciurines (=basal aplodontids) that are more common from earlier horizons and fewer, generally more poorly represented species referable to the otherwise Arikareean genera, Allomys, Downsimus, and Niglarodon. The species of these genera from Blue Ash, Allomys sp., Downsimus sp., and N. brachyodon, differ from all other recognized species of these genera in being smaller with more primitive cheek tooth morphologies.