A New Middle Pleistocene Species ofMicrotus (Pedomys)From the Southern United States, with Comments on the Taxonomy and Early Evolution ofPedomysandPitymysin North America

Abstract

Microtus (Pedomys) australis, sp. nov., is described from the Haile XVIA local fauna (1. f.) of Florida (ca. 1.3 to 1.6 Ma [million years ago]) and the Vera 1. 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 subsumed under M. pliocaenicus. The sample on which this taxon was based, from Cumberland Cave, is referred to as M. pliocaenicus/guildayi, a slightly modified form of the informal taxonomic usage proposed by Krishtalka and Stucky (1985). Microtus llanensis is synonymized with M. ochrogaster and is recognized as M. o./llanensis. It is considered an intermediate in the phyletic sequence from M. p. /guildayi to modern M. ochrogaster. Specimens reported by Repenning and Grady (1988) from the middle Pleistocene Hamilton Cave 1. f. as Pitymys hibbardi do not belong to that taxon and may represent a new species. Pitymys hibbardi is treated as a large form in a phyletic sequence leading to extant M. pinetorum. The Pleistocene replacement chronology of “pitymyinine” voles in Florida is as follows: M. australis-M. aratai-M. pinetorum/hibbardi-M. pinetorum/parvulus. A cladistic analysis of dental characters for select subgenera of Microtus is presented, and a revised classification is offered. Orthriomys, Pitymys, and Pedomys are recognized as endemic North American subgenera of Microtus, while representatives of Phaiomys (M. pliocaenicus) and Terricola (M. meadensis) are considered to be Old World immigrants. The relationships of M. quasiater, M. oaxacensis, M. guatemalensis, and M. aratai remain obscure.