Oryzomyini. Diagnosed as a subgenus of Oryzomys to segregate arboreal, pencil-tailed sigmodontines with a long palate from Rhipidomys, under which many of the species included here were first described. Thereafter treated alternatively as a subgenus of Oryzomys (Ellerman, 1941; Goldman, 1918) or as full genus (Gyldenstolpe, 1932; Thomas, 1917c) until Hershkovitz's (1960) revision stabilized its ranking as a subgenus (e.g., Cabrera, 1961; Hall, 1981). Systematists have recently acknowledged the morphological and karyotypic distinctiveness of Oecomys at the generic level (Andrades-Miranda et al., 2001b; Carleton and Musser, 1984; Gardner and Patton, 1976; Reig, 1984, 1986); species so far surveyed genetically are reciprocally monophyletic with other oryzomyine genera (Smith and Patton, 1999; Weksler, 2003) but broader phylogenetic substantiation is desirable.
Revised by Hershkovitz (1960), who consolidated some 25 species (e.g., Ellerman, 1941; Gyldenstolpe, 1932) into just two, bicolor and concolor. Although this gross underestimation of specific diversity within Oecomys has been intimated by other authors (e.g., Gardner and Patton, 1976; Reig, 1986), it has yet to be documented within a full taxonomic revision. The species identified here mainly repeat those compiled by Musser and Carleton (1993), based on a (still) unfinished revision; while all of these will stand as valid, some, such as O. bicolor and O. trinitatis, are undoubtedly composites even now. Morphological and karyotypic comparisons of species in W Brazil (Patton et al., 2000) and French Guiana (Voss et al., 2001) underscore the far greater local biodiversity that was masked by Hershkovitz’s (1960) interpretation and supply regional glimpses of the species richness within the Neotropical realm yet to be fully understood.