A NEW MIDDLE PLEISTOCENE SPECIES OF MICROTUS (PEDOMYS) FROM THE SOUTHERN UNITED-STATES, WITH COMMENTS ON THE TAXONOMY AND EARLY EVOLUTION OF PEDOMYS AND PITYMYS IN NORTH-AMERICA

Microtus (Pedomys) australis, sp. nov., is described from the Haile XV IA local fauna (l.f.) of Florida (ca. 1.3 to 1.6 Ma [million years ago ]) and the Vera l.f. of Texas (ca. 0.6 Ma)-Microtus australis shares a number of plesiomorphic features with M. pliocaenicus and is related to both the subgenus Phaiomys, from which it evolved, and the subgenus Pedomys, to which it is referred. Microtus (Pedomys) guildayi is subs umed under M. pliocaenicus. The sample on which this taxon was based, from Cumberland Cave, is referred to as M. pliocaenicus/guildayi, a sl ightly modified form of the informal taxonomic usage proposed by Krish talka and Stucky (1985). Microtus llanensis is synonymized with M. och rogaster and is recognized as M. o./llanensis. It is considered an int ermediate in the phyletic sequence from M. p./guildayi to modern M. oc hrogaster. Specimens reported by Repenning and Grady (1988) from the m iddle Pleistocene Hamilton Cave l.f. as Pitymys hibbardi do not belong to that taxon and may represent a new species. Pitymys hibbardi is tr eated as a large form in a phyletic sequence leading to extant M. pine torum. The Pleistocene replacement chronology of ''pitymyinine'' voles in Florida is as follows: M. australis-M. aratai-M. pinetorum/hibbard i-M. pinetorum/parvulus. A cladistic analysis of dental characters for select subgenera of Microtus is presented, and a revised classificati on is offered. Orthriomys, Pitymys, and Pedomys are recognized as ende mic North American subgenera of Microtus, while representatives of Pha iomys (M. pliocaenicus) and Terricola (M. meadensis) are considered to be Old World immigrants. The relationships of M. quasiater, M. oaxace nsis, M. guatemalensis, and M. aratai remain obscure.