Arvicolini, subtribe Arvicolina (Pavlinov et al., 1995a). We provisionally retain Chionomys in Arvicolini, following Gromov and Polyakov (1977), but stress that its tribal affinities are unresolved. Others have viewed the genus as a member of Myodini, as based on allozymic data (Mezhzherin et al., 1995) or on the stratigraphic sequence of fossils that suggest common ancestry with Myodes (Kretzoi, 1969; Chaline, 1987).
Miller (1912a), although describing Chionomys as a genus, later employed it as subgenus, a status that became entrenched in the literature (Chaline et al., 1999; Corbet, 1978c; Krapp, 1982a; Neuhäuser, 1936) with rare dissent (e.g., Gromov and Polyakov, 1977). A diverse information base, however, depicts Chionomys as a lineage apart from Microtus (Chaline and Graf, 1988; Graf, 1982; Krytufek, 1999c; Mezhzherin et al., 1993, 1995; Nadachowski, 1990a; Pavlinov and Rossolimo, 1987, 1998; Pavlinov et al., 1995a; Zagorodnyuk, 1990). Van der Meulen (1978) considered Suranomys to be a junior synonym, but the type species of Suranomys (= Microtus malei) is related to the Microtus oeconomus group, not to Chionomys (Nadachowski, 1990a). New World Microtus longicaudus was referred to Chionomys by Anderson (1960), but a variety of data sources allies the former with Microtus proper (Chaline and Graf, 1988; Conroy and Cook, 1999, 2000; Graf, 1982).
Gromov and Polyakov (1977) provided detailed morphological and geographical descriptions of Chionomys and its three species, which they viewed as distinctive montane forms with ecologies convergent to those of Alticola and Dinaromys. Karyotypic variation is reported by Sablina et al. (1988) and Zima and Kral (1984a). Nadachowski (1991) discussed the systematics, geographic variation and evolution of Chionomys species based on dental traits. Krytufek (1999c:335) remarked that snow voles "live in a narrow band of the south-western Palaearctic which is approximately 5500 km long and up to 2500 km broad." All three species are sympatric in the Pontic Mtns, NE Turkey and the Caucasus (Krytufek, 1999c; Nadachowski, 1990a), and they also occurred there during the Pleistocene (Nadachowski and Baryshnikov, 1991). Nadachowski (1990a, 1991) suggested that C. nivalis evolved in Europe by the late Pleistocene and the others evolved in the Caucasus-Near East region, with C. roberti splitting from a gud-roberti ancestral stock by middle Pleistocene. Krytufek (1999c) considered this hypothesized speciation in light of Pleistocene sea level oscillations around the Bosphorous landbridge and their vicariant effect (see Hosey, 1982).