Phyllotini. Morphologically similar to Calomys (Hershkovitz, 1962; Williams and Mares, 1978), but cladistic interpretations of morphological and molecular data represent the genus as more highly derived, usually as a basal clade to Phyllotis and various kin depending upon the taxa sampled (Braun, 1993; Engel et al., 1998; Spotorno et al., 2001; Steppan, 1993; Smith and Patton, 1999).
Revised by Hershkovitz (1962), who synonymized all forms as E. typus, but morphological, chromosomal, and distributional evidence supports greater species diversity (e.g., Kelt et al., 1991; Mann, 1978; Mares et al., 1989b; Osgood, 1943; Zambelli et al., 1992). The thrust of recent revisionary research has overwhelmingly reinforced the latter view (Hillyard et al., 1997; Sikes et al., 1997; Sportorno et al., 1994; Tiranti, 1997) and collectively indicates the number of species as at least four. Others are occasionally listed (Braun, 1993; Díaz and Barquez, 1999; Galliari et al., 1996) or noted as species indeterminate (Mares et al., 1997), a situation that underscores the need for continued revision. Tiranti (1997) viewed the northern (E. moreni E. puerulus) and southern (E. morgani E. typus) pairs as sister clades and offered a Plio-Pleistocene biogeographic interpretation to explain their phyletic diversification.