Rodents (Mammalia) from Fitterer Ranch, Brule Formation (Oligocene), North Dakota

Eighteen rodent species are recognized from the Fitterer Ranch fauna of North Dakota on the basis of more than a thousand collected specimens. Of the species recognized, four are new: the prosciurine aplodontiids Prosciurus hogansoni and Altasciurus leonardi, the heliscomyid Heliscomys borealis, and the cricetid Eumys lammersi.
A previously described castorid from this fauna, Oligotheriomys primus Korth, 1998, is considered a synonym of “Eutypomysmagnus Wood, 1937, on the basis of the recovery of lower dentitions but is retained in the genus Oligotheriomys. A single specimen is questionably referred to Microparamys, a genus elsewhere limited to the Eocene (Clarkforkian-Chadronian land mammal ages). The rodent fauna appears to be a combination of predominantly Orellan and Whitneyan species (early Oligocene), suggesting that the section might transcend the Orellan-Whitneyan boundary. However, the rodent fauna does not alter significantly from the lowest to the highest horizons.