RODENTS (MAMMALIA) FROM THE WHITNEYAN (MIDDLE OLIGOCENE) CEDAR PASS FAUNA OF SOUTH DAKOTA

Twenty species of rodents are recognized from the early Whitneyan Cedar Pass Fauna of South Dakota. Two new species are recognized, the sciurid Douglassciurus bjorki (including specimens originally referred to Cedromus wilsoni Korth and Emry, 1991, from the late Whitneyan Blue Ash Fauna) and the cricetid Paciculus cedrus. Due to a more complete record at Cedar Pass, the florentiamyid Hitonkala martintau Korth, 2008, is allocated to the genus Kirkomys Wahlert, 1984 as a new combination, Kirkomys martintau (Korth, 2008). The new sample of this species also allows for a description of the complete cranium of Kirkomys previously only known from a single partial skull. Among the genera of rodents identified from Cedar Pass, two earlier occurring genera have their last occurrence and six later occurring genera have their first occurrence. Thirteen genera that extend into the Arikareean present in the later Whitneyan Blue Ash Fauna are lacking in the Cedar Pass Fauna. Only one genus of rodent is limited to the Whitneyan, Disallows Korth, 2009a. This demonstrates that the age represented by the fauna at Cedar Pass is transitional between the Orellan and later Whitneyan horizons. The proportions of rodents (relative number of specimens and species) also differ between the Cedar Pass and the Blue Ash faunas, again, indicating an earlier age for the Cedar Pass Fauna.