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A NEW SPECIES OF ANSOMYS (RODENTIA, APLODONTIDAE) FROM THE LATE OLIGOCENE (LATEST WHITNEYAN-EARLIEST ARIKAREEAN) OF SOUTH DAKOTA

Hopkins (2004) recently reviewed the species of Ansomys Qiu (1987). She recognized only two species from North America, A. nexodens (Korth, 1992) from the Orellan (early Oligocene) of Montana, and A. hepburnensis Hopkins (2004) from the Barstovian (middle Miocene), also of Montana. This left a considerable time gap between the known record of North American species, which led her to suggest a series of migration events between Eurasia and North America throughout the Tertiary. Recently, Kelly and Korth (2005) named an additional species of Ansomys, A. nevadensis from the Hemingfordian (early Miocene) of Nevada, thus partially filling the time gap between the previously described North American species. Kelly and Korth (2005), however, noted that A. nevadensis was morphologically closer to the Asian middle Miocene species A. orientalis Qiu (1987) rather than the other North American species. The fossil specimens described below are from the latest Whitneyan or earliest Arikareean of South Dakota (late Oligocene), once again, filling another time gap in the North American record of Ansomys. They also represent the easternmost occurrence of the genus in North America. Dental terminology used follows that of Wood and Wilson (1936) with modifications of Rensberger (1975). All specimens cited are part of the research collections at the Carnegie Museum of Natural History (CM).