Earlier associated either with Palearctic hamsters in Cricetinae (e.g., Corbet, 1978c; Corbet and Hill, 1991; Ellerman and Morrison-Scott, 1951) or with the New World neotomine Peromyscus (Ellerman, 1941, 1961). Nomenclatural association with Palaearctic hamsters seemed to reflect more the uncertainty and indecision concerning its relationships rather than conviction of its membership in Palearctic Cricetinae (Carleton and Musser, 1984; Corbet, 1978c). On the other hand, Ellerman (1941) did not question the close phyletic grouping of Calomyscus and Peromyscus, and Osgood (1947:166) even viewed it as being "so similar to the American Peromyscus that it probably signifies a late Pleistocene invasion from North America." An alliance with New World species was echoed by Pavlinov (1980c), who retained Calomyscus with neotomines because of close similarities between it and Reithrodontomys in morphology of the auditory ossicles. Graphodatsky et al. (2000:303) noted that conventionally stained and banded karyotypes of Calomyscus actually resemble those of Peromyscus, "particularly in the presence and variation of the heterochromatic small arms," but they did not discover clear G-band homologies between the two.
After comprehensive review of morphological systems, Vorontsov and Potapova (1979) recognized Calomyscus’ distinctive combination of features by setting it apart as a tribe in the subfamily Cricetinae, Cricetidae (elevated to subfamily in an inclusive Muridae by Musser and Carleton, 1993). Agusti (1989:387) regarded Calomyscus as the only living member of the Myocricetodontinae, an allocation supported only by this statement: "We also consider the genus Calomyscus as belonging to the Myocricetodontinae." His action has been followed by researchers reporting isolated fossil teeth identified as species of Myocricetodontinae (e. g., Agustí and Casanovas-Villar, 2003; Wessels, 1996, 1998, 1999). Wessels (1998) also included the South African Mystromys (the sole living member of Mystromyinae; see that account) within the Myocricetodontinae, which he arranged within Gerbillidae. We compared molar occlusal patterns of living species of Calomyscus with published illustrations of various myocricetodontines and cannot appreciate the resemblance indicated by Agusti and Wessels. No critical study exists supporting either Agusti’s allocation, and the subsequent arrangements based upon it, or Fahlbusch’s (1969) earlier suggested derivation of Calomyscus from the Miocene Democricetodon.
The cladistic isolation of Calomyscus within Muroidea has been recently supported by phylogenetic analyses of nuclear DNA sequences (Michaux et al., 2001b). Calomyscus emerges as the sole member of a clade removed from the lineage including Mystromys (Nesomyidae) and basal to those radiations representing Cricetidae and Muridae. Until further studies refine the preliminary morphological and molecular evidence, family status for Calomyscus is an interim nomenclatural treatment that reflects its relationships as so far understood.
Several extinct species of Calomyscus have been recovered from late Miocene strata in Turkey, Spain, and France, and early Pliocene beds on Rhodes (see reviews by Agustí and Casanovas-Vilar, 2003; Wessels, 1998, 1999); origin of the genus certainly occurred earlier. Species of Calomyscus are generally known as "mouse-like hamsters" (Wilson and Cole, 2000), which unfortunately perpetuates its inaccurate association with true hamsters in subfamily Cricetinae. The Greek kalos means beautiful and the generic name translates as "beautiful mouse," an improvement over "mouse-like hamster" and one implicit in using Calomyscus as part of the common name.