Arvicolini. Included in Pitymyini by Repenning et al. (1990) and Repenning (1992). Maintained as a genus by some specialists (Ellerman, 1941; Hinton, 1923, 1926a; Zagorodnyuk, 1990, 1992c), as a subgenus of Pitymys by others (Corbet, 1978c; Ellerman, 1941; Ellerman and Morrison-Scott, 1951), or a subgenus of Microtus (G. M. Allen, 1940; Gromov and Erjabeva, 1995; Gromov and Polyakov, 1977; Musser and Carleton, 1993; Pavlinov et al., 1995a). Hinton (1923, 1926a) enumerated cranial traits that characterize Neodon and considered it to be closely related to Pitymys, primarily based on the m1 occlusal pattern; species of Nearctic Pitymys and Palearctic Terricola (here treated as subgenera of Microtus) and Neodon sikimensis all possess this pitymyine m1 configuration (as defined by Repenning, 1992:65). Both N. sikimensis and pitymyine forms also have an elongate and complex M3, generally with four lingual salient angles in contrast to the simpler pattern seen in Phaiomys leucurus (see Hinton, 1923, 1926a; Nadachowski and Zagorodnyuk, 1996; Repenning, 1992). Hinton (1923) included forresti, irene, oniscus (= irene), and carruthersi (= juldaschi) in Neodon. Occlusal patterns of their m1s vary, some similar to the pattern in N. sikimensis, others less complex and generally, but not in detail, resembling the Allophaiomys like configuration as seen in Blanfordimys and Phaiomys (specimens in AMNH, FMNH, and USNM; also see Nadachowski and Zagorodnyuk, 1996). All have a more elaborate M3 than that in Phaiomys leucurus, and none possesses the deep and stout cranium like that species or its short, constricted incisive foramina (see account of P. leucurus).
Species of Neodon (along with Blanfordimys and Phaiomys) are characterized as Pleistocene relicts because their molar occlusal patterns resemble the extinct Allophaiomys. Further, one species (N. juldaschi) has a primitive karyotype similar to that hypothesized as ancestral to Arvicolini (2n = 56, Chaline and Matthey, 1971; or 2n = 54, Zagorodnyuk, 1992c). Thus, Nadachowski and Zagorodnyuk (1996:387) viewed these voles as "Allophaiomys like" species that represent "Pleistocene relicts or a return to an initial type," with ranges in C and S Asia at the austral periphery of the Palearctic arvicoline distribution. We provisionally retain Neodon as a lineage independent of Phaiomys and Microtus until phylogenetic relationships can be analyzed by a suite of information bases, including morphological traits other than molar patterns.