The cricetid-murid question has persisted as the dominant theme, or uncertainty, involving the higher level classification of muroid rodents over the past century (see summaries in Carleton, 1980, and Carleton and Musser, 1984): in essence, should the various subfamilies be approximately equally apportioned between Cricetidae and Muridae (Miller and Gidley, 1918; Simpson, 1945) or should most be placed under an all encompassing Muridae (Alston, 1876; Ellerman, 1940; Thomas, 1896—even these studies, however, accorded the fossorially specialized forms separate familial rank; i.e., the spalacines, rhizomyines, and myospalacines in various combinations). While the inclusive view of Muridae has gained acceptance over the latter half of the 20th century (Hershkovitz, 1962; Hooper and Musser, 1964a; McKenna and Bell, 1997), there are notable departures (Chaline et al., 1977; Lavocat, 1978), and Reig (1980, 1981, 1984), in particular, has steadfastly espoused recognition of a separate Cricetidae, the contents of which correspond in large part to the taxa covered here. Principal subfamilial exceptions to Reig’s coverage are exclusion of certain African clades (Cricetomyinae, Dendromurinae, Nesomyinae), here arranged in a broadly defined Nesomyidae (as per Lavocat, 1973, 1978), and inclusion of Arvicolinae and Lophiomyinae, each of which Reig regarded as separate families. Accepting those adjustments, monophyly of the family finds general support in phylogenetic evaluation of genetic sequence data (Dubois et al., 1999; Michaux and Catzeflis, 2000; Michaux et al., 2001b; Robinson et al., 1997). Nevertheless, this cladistic hypothesis of Cricetidae should be viewed as provisional, and taxonomic sampling must be considerably expanded to reinforce its validity, notably with addition of groups such as Lophiomyinae and many more cladistically older members drawn from Cricetinae, Sigmodontinae, and Tylomyinae.
Although monophyletic on molecular trees, unambiguous diagnosis of so large and heterogeneous an assemblage would prove challenging with the morphological character base currently referenced in phylogenetic studies. We note that all members possess a biserial arrangement of the molar cusps, with retention of a longitudinal connection (mure/murid) among them and formation of a discrete anterocone(id) on the first molars. Such character states are likely ancestral for the superfamily, as are other traits exhibited by many cricetid species, in some cases a majority of them (three-rooted upper and two-rooted lower molars; possession of mesolophs(ids); malleus configuration parallel; tegmen tympani conformation; complete carotid circulatory pattern; entepicondylar foramen present; stomach unilocular-hemiglandular; full complement of male reproductive glands). However, parallel evolution of derived conditions for each of these characters is apparent at lower taxonomic levels within Cricetidae (subfamilies and tribes) and among other families of Muroidea as currently understood.
The fossil record of "cricetids" is comparatively rich in taxa, deep in time, and broad in geographic representation, and their phylogenetic systematics is correspondingly complicated. Several groups—e.g., cricetodontines, eucricetodontines, paracricetodontines, and cricetopines—have been variously acknowledged as families separate from Cricetidae; McKenna and Bell (1997) recapitulated family-group rankings used for such extinct cricetids and retained most as tribes or subfamilies within Muridae sensu lato. Also see overview by Carleton and Musser (1984) and regional treatments by Freudenthal et al. (1992), Hugueney (1999), Kälin (1999), Korth (1994), Lavocat (1978), Martin (1980), Mein and Freudenthal (1971), and Rümmel (1999). The evolutionary fate of many of these extinct groups as progenitor to living cricetid assemblages is generally unclear and-or much disputed; where some phyletic link is plausibly documented, usually not until Miocene in age, we mention those groups in the subfamily comments. Geological range from the early Oligocene to Recent of Europe, late Eocene to Recent of Asia, late Miocene to Recent of Africa, late Eocene to Recent of North America, and early Pliocene to Recent of South America (McKenna and Bell, 1997).