Oligoryzomys Bangs, 1900

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 132

Oligoryzomys Bangs, 1900

Pygmy rice rats

The pygmy rice rats are a speciose but poorly known group that is widely distributed throughout the Neotropical Realm, from southern México to Tierra del Fuego and to eastern Amazonia and the Mata Atlântica of coastal Brazil (Carleton and Musser, 1989; Emmons and Feer, 1997). Over this enormous range, member species may be common within habitats spanning lowland tropical forest to the high Andean puna grasslands or páramo above timberline. Often placed as a subgenus within Oryzomys by earlier workers, its generic status was solidified by Carleton and Musser (1989), who provide an emended diagnosis as well as a provisional list of species with generalized descriptions and geographic ranges. Their diagnosis includes, but is not limited to, the following traits: small body size; tail usually longer than head and body; six plantar tubercles, with hypothenar pad small and round; skull small but stout in appearance; rostrum relatively broad and stocky; interorbital region hourglass shaped with squared edges; braincase elongate, smooth, and flat, with foramen magnum directed posteriorly; zygomatic arches bowed laterally; jugal reduced or absent; zygomatic notches distinct; zygomatic plates broad, with the anterior edge reaching the nasolacrimal capsules; stapedial foramen large, posterior opening of alisphenoid canal large, squamosal­alisphenoid groove and sphenofrontal foramen absent (derived cephalic arterial supply; pattern 2 of Voss, 1988; Carleton and Musser, 1989); incisors opisthodont, asulcate; molars brachydont, cuspidate, with three roots in uppers and two in lowers; first molars ovate, anteromedian flexus (­id) shallow, anterolabial and anterolingual conules (­ids) small, anteroloph and mesoloph (­id) present; anterolabial cingulum well developed on lower third molar.