Microtus Schrank, 1798 . Fauna Boica, 1 (1):72.

TYPE SPECIES: Microtus terrestris Schrank, 1798 (= Mus arvalis Pallas, 1778).

SYNONYMS: Agricola, Alexandromys, Ammomys, Arbusticola, Arvalomys, Aulacomys, Campicola, Chilotus, Euarvicola, Hemiotomys, Herpetomys, Iberomys, Lemmimicrotus, Meridiopitymys, Micrurus, Mynomes, Neodon, Orthriomys, Pallasiinus, Parapitymys, Pedomys, Phaiomys, Pinemys, Pitymys, Psammomys (of Le Conte, 1830, not Cretzschmar, 1828), Stenocranius, Sumeriomys, Suranomys, Sylvicola, Terricola, Tetramerodon.

COMMENTS: Nowhere are the explosiveness and recency of arvicoline evolution more dramatically highlighted than by the inconsistency of systematic treatment of genusgroup taxa to be subsumed by Microtus . No consensus exists concerning the morphological limits or monophyly of many of these taxa, a situation which in part reflects the narrow reliance of our classifications on dental characters undergoing rapid change (see Guthrie, 1971; Koenigswald, 1980). Such variability and inconsistency of systematic opinion are epitomized by the taxon Pitymys . As noted by Carleton and Musser (1984:321), "Generally, paleontologists and European mammalogists accord Pitymys separate generic status (Corbet, 1978c; Koenigswald, 1980; Repenning, 1983), whereas North American workers view it as a subgenus of Microtus (Hall, 1981; Jones et al., 1975)." The geographic split among systematists is by itself instructive, as is the nature of the character base consulted by paleontologists versus neontologists. Similar disputes have surrounded the taxonomic history of other genus-group taxa associated with Microtus, such as Arvicola, Blanfordimys, Chionomys, Lasiopodomys, Neodon, Phaiomys, and Proedromys.

Zagorodnyuk (1990) developed an interesting reclassification of Microtus and its kin. Although probably wrong on details, we believe that it offers an important philosophical alternative in the continuing examination of relationships among Microtus-like forms. In his arrangement of Arvicolini, Zagorodnyuk emphasized hypotheses of intracontinental origin and regional diversification of major clades of Microtus . Thus, pitymyine forms of the Old World (Terricola) are segregated from those of the New World (Pitymys); New World common voles (Mynomes) are separated from Old World voles such as Microtus proper, Alexandromys, and Agricola; and the invasion of the New World semiaquatic niche is recognized (Aulacomys) as independent of the Old World water-vole radiation (Arvicola). If we interpret them correctly, such a viewpoint is consistent with the preliminary results emerging from electrophoretic studies (Chaline and Graf, 1988; Graf, 1982; Moore and Janecek, 1990) and with some paleontological perspectives (e.g., Chaline, 1974). The more traditional notion of intercontinental dispersal and broad transcontinental distributions still receives stong support in the publications of Martin (1974, 1987), Repenning (1980, 1983), Repenning et al. (1990), and van der Muelen (1978). Although we question Zagorodnyuk's cardinal reliance on chomosomal traits and do not wholly embrace his ranking of taxa (e.g., Neodon and Terricola as genera), his classification of Microtus and related forms deserves serious attention in future studies.

See accounts of Blanfordimys, Chionomys, Lasiopodomys, and Proedromys, often included in Microtus but which are here treated as genera. North American forms revised by Bailey (1900) and taxonomy updated by Hall and Cockrum (1953) and Hall (1981); many aspects of paleontology, taxonomy, zoogeography, and anatomy covered in Tamarin (1985). For synoptic coverage of the more diverse Palearctic Microtus fauna, see Corbet (1978c), Gromov and Polyakov (1977), Niethammer and Krapp (1982a), and Ognev (1963b, 1964).