Oryzomys Baird, 1857

VOSS, ROBERT S., LUNDE, DARRIN P. & SIMMONS, NANCY B., 2001, The Mammals Of Paracou, French Guiana: A Neotropical Lowland Rainforest Fauna Part 2. Nonvolant Species, Bulletin of the American Museum of Natural History 2001 (263), pp. 1-236 : 120

Oryzomys Baird

The Amazonian species of Oryzomys were recently revised by Musser et al. (1998), whose species­level taxonomy is followed herein. As a group, Amazonian species of Oryzomys are easily distinguished from other sympatric rodents by external characters. These are medium­sized murids, ranging in average adult body weight from about 40 to 80 g. The dorsal fur is soft (not spiny) and varies in color (depending on species, age, and stage of molt) from rich reddish or tawny hues to drab brown. The ventral fur is superficially whitish or whitish gray, contrasting abruptly in color with the dorsal fur (ex­ cept in juveniles), but the ventral hair bases are always dark gray. The mystacial vibrissae are short, not extending beyond the tips of the pinnae when laid back alongside the head. The dorsal surface of the hindfoot is unmarked by dark metatarsal spots or bands, and the naked plantar surface is pigmented (grayish in life and in fluid­preserved material, blackish on dried skins). The hindfoot (fig. 53A) appears narrow because the three central pedal digits (II, III, and IV) are much longer than the outer digits (I and V); the fifth digit is not semi­opposable (its claw not extending to the end of the first phalange of dIV). Tails are usually at least partially bicolored (at least near the base), average about as long as (never much shorter or longer than) the combined length of head­and­body, and appear quite naked (a sparse caudal pelage is visible only under magnification). Contrasting external characters of Oecomys species , which are sometimes misidentified as Oryzomys (and vice versa) by fieldworkers, are given in the introductory account for that genus (above).

Three species, Oryzomys macconnelli , O. megacephalus , and O. yunganus , occur sympatrically at Paracou as they probably do throughout the Guiana subregion of Amazonia (see range maps in Musser et al., 1998). Whereas adult specimens of O. macconnelli are easily recognized by external characters, accurate field identifications of O. megacephalus and O. yunganus are more difficult. Juvenile Oryzomys , which lack the diagnostic external dimensions and coloration of adults, cannot be reliably identified in the field.