Aplodontid rodents (Mammalia) from the Oligocene (Orellan and Whitneyan) Brule Formation, Nebraska

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Abstract
Seven species of aplodontid rodents are recognized from the Orellan, four from the Whitneyan, and one from both horizons of Nebraska. Three new genera are recognized, Epeiromys from the Orellan, Oropyctis from the Whitneyan, and Campestrallomys from both horizons. Three new Orellan species (Prosciurus parvus, Campestrallomys annectens, and Epeiromys spanius), two new Whitneyan species (Oropyctis pediasius and Campestrallomys siouxensis), and one new species from the late Orellan and early Whitneyan (Prosciurus magnus) are described. An indeterminate species of aplodontid from the Whitneyan is also recognized. Only a few lineages of aplodontids can be traced from the Orellan into later times. Campestrallomys, Downsimus, and Haplomys can be derived from Prosciurus. Oropyctis may represent an early ancestor of the Mylagaulidae, but this relationship is quite tenuous. The biostratigraphic occurrence of several species of aplodontids in Nebraska suggests that all species are not continuous throughout the Orellan of Nebraska, and that these species may be useful as biostratigraphic markers.