Mammals from the Blue Ash Local Fauna (late Oligocene), South Dakota. Rodentia, Part 2: Families Florentiamyidae and Geomyidae

Three species of florentiamyid, Florentiamys sp. cf. F. kingi Wahlert, Kirkomys parvus (Troxell), and Hitonkala martintau n. sp., and an undetermined species of geomyid are recognized from the Blue Ash fauna. This increases the total number of rodents described from this fauna to 14. Florentiamys sp. cf. F. kingi is similar in morphology to the Arikareean F. kingi, but is slightly smaller. This is the first record of Kirkomys parvus other than the holotype, which is known from an uncertain horizon. Hitonkala martintau is distinct from the previously known Arikareean species of the genus by its more primitive cheek tooth morphology (smaller stylar cusps on upper molars; less molariform premolars). Specimens of the undetermined geomyid cannot be assigned to any currently known species of geomyoid from either the Arikareean or earlier. The smaller size of Florentiamys sp. cf. F. kingi and more primitive dental morphology of Hitonkala martintau compared to similar Arikareean species suggest that the fauna is of very earliest Arikareean age or perhaps latest Whitneyan.