MURIDAE ILLIGER, 1815

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 : 90

MURIDAE ILLIGER, 1815

SIGMODONTINAE WAGNER, 1843

Rats and mice of this family (subfamily Sigmodontinae ) possess three cheekteeth and a myomorphic masseter muscle system coupled with a sciurognathus lower jaw. Those that occur within the Rio Juruá basin include a diverse set of arboreal and terrestrial taxa ranging in body size from quite small (20 grams) to very large (more than 250 grams). Some are habitat specialists, others have extremely broad ecological ranges. Two genera ( Holochilus and Nectomys ) are found primarily in inundated areas or along stream banks, as they readily enter water; two genera are either semiarboreal ( Oecomys ) or almost strictly arboreal ( Rhipidomys ); three are terrestrial and small­bodied, two with distinctly spinose fur ( Neacomys and Scolomys ) and the third with an extremely long tail ( Oligoryzomys ); and, finally, one is an ‘‘average­sized’’ terrestrial mouse (the ubiquitous Oryzomys ). All but one of these genera are currently placed in the presumptively monophyletic tribe Oryzomyini (sensu Voss and Carleton, 1993) ; the remaining genus, Rhipidomys , is usually placed in the ‘‘ Thomasomyini ,’’ a collection of genera apparently united only by shared primitive features (Voss, 1993). As a group, this assemblage of genera is rather characteristic of most lowland faunas of Amazonia, particularly of the western regions of southern Colombia south to northern Bolivia and east into central Brazil.

Some of these genera and many species are difficult to distinguish, especially for individuals without access to adequately curat­ ed and identified museum collections. To assist proper identification, we describe and figure the skull of each genus and most species in the accounts below, and summarize their patterns of morphological and molecular variation throughout the Rio Juruá and elsewhere in Amazonia. We refer readers to the keys presented by Emmons and Feer (1997) and Anderson (1997) as well as to recently published revisions (Carleton and Musser, 1989; Musser et al., 1998; Voss and Carleton, 1993) for further help in identifying these genera.

TRIBE ORYZOMYINI VORONTSOV