Oryzomys perenensis J. A. Allen 1901

Oryzomys perenensis J. A. Allen 1901, Bull. Am. Mus. Nat. Hist., 14: 406.

Type Locality: Perú, Junín Dept., Perené, 800 m.

Vernacular Names: Western Amazonian Oryzomys.

Distribution: E Andean foothills and western margins of the Amazon Basin, including C and SE Colombia, E Ecuador, E Perú, E Bolivia, and WC Brazil (see Patton et al., 2000:Fig. 96); eastern limits indeterminate.

Discussion: Morphometric and karyotypic differentiation of western Amazonian populations (perenensis) from eastern ones (O. megacephalus sensu stricto) recognized by Musser et al. (1998), who doggedly elected to retain the former as a synonym of the latter pending vouchered demonstration of sympatry. Genetic divergence persuasively documented by Patton et al. (2000), who reinstated O. perenensis as a species, as have others (Bonvicino and Martins Moreira, 2001; Voss et al., 2001). Eastern distributional limits, however, remain obscure and undocumented by specimens; given the morphological ambiguity of certain series from middle Amazonas (see Musser et al., 1998), the stature and geographic limits of perenensis should continue to be refined with regard to western populations of O. megacephalus.