Rodents and lagomorphs (Mammalia) from the Late Clarendonian (Miocene) AshHollow Formation, Brown County, Nebraska

Twenty-five species of rodents and lagomorphs are recognized from Pratt Qua rry, Brown County, Nebraska. Of these, four are new: the beaver Dipoides ta nneri, the heteromyid Cupidinimus prattensis, the cricetid Antecalomys phth anus (also new genus), and the leporid Pronotolagus whitei. The rodent and lagomorph fauna from Pratt Quarry is clearly transitional be tween Clarendonian and Hemphillian because it contains the first record of four typically Hemphillian taxa (Dipoides, sigmodontine cricetids, Hypolagu s vetus, leporine leporids), and the last record of eight Clarendonian or e arlier taxa (Protospermophilus, Petauristodon, Eucastor, Phelosaccomys, Mio heteromys, Copemys, Tregomys, and Hesperolagomys). This combination of firs t and last occurrences verifies a latest Clarendonian age for the fauna and the Merritt Dam Member of the Ash Hollow Formation.