Oryzomys (Oligoryzomys) chacoensis Myers & Carleton, 1981 Cricetidae Don E. Wilson Russell A. Mittermeier Thomas E. Lacher, Jr 496XH Bangs 1900 [2142,2569,636,682] Mammalia Cricetidae Oligoryzomys Animalia Rodentia 157 436 Chordata species chacoensis    444.    Chacoan Pygmy Rice Rat    French: Colilargo du Chaco/ German: Chaco-Zwergreisratte/ Spanish: Rata arrocera pigmea del Chaco   Other common names: Chacoan Colilargo   Taxonomy. Oryzomys (Oligoryzomys) chacoensis Myers & Carleton, 1981,  “ 419 kmby road NW Villa Hayes (alongside the Trans Chaco Highway), Dept. Boqueron,  Paraguay.”This species is monotypic.    Distribution.SE Bolivia, SW Brazil, W & C Paraguay, and N Argentina.   Descriptive notes.Head-body 97 mm,tail 105-150 mm, ear 13-19 mm, hindfoot 18-30 mm; weight 25 g. Dorsum of the Chacoan Pygmy Rice Rat is clay-colored, heavily lined with black, and darkest over shoulders; head is grayer, very heavily lined with black; cheeks are brown or gray, occasionally with some orange; sides are lighter; and venter contrasts sharply with sides and is white or occasionally washed buffy, with basal one-half of hairs plumbeous, except on chin and throat where hairs are white to base. Old individuals are deep reddish brown, and dorsum is less heavily lined with black. Pelage of young is woollier and grayer butstill strongly brown, and lining of back is less distinct. Tail is weakly bicolored and averages 131% (range 112-171%) of head-body length. Feet average 25% (range 19-32%) of head-body length. Pinnae are heavily furred inside and averaged 69% (52-83%) of hindfoot length; hairs are orangish over most of their lengths (basal 33% orless dark); and distinctive tufts of orangish hairs are usuallyjust anterior to ear notch. Chromosomal complement is 2n = 58, FN = 74.   Habitat.Forest, thornscrub, and grassland in Chaco ecoregion of South America. The Chacoan Pygmy Rice Rat has an affinity for sites with trees and shrubs.   Food and Feeding.Chacoan Pygmy Rice Rats are granivorous and frugivorous.   Breeding.Two Chacoan Pygmy Rice Rats caught in September had three embryos each; another one had five embryos. Juveniles were caught in February and September. Lactating females were caught in April and July; males with abdominal testes were caught in May-August, and one male with scrotal testes was caught in May. Shedding were observed in May and July.   Activity patterns.The Chacoan Pygmy Rice Rat is crepuscular and nocturnal. It is mainly terrestrial; although most individuals are commonly found on the ground, some were found on trees up to 10 m or more above the forest floor.   Movements, Home range and Social organization.No information.   Status and Conservation.Classified as Least Concern on The IUCN Red List. The Chacoan Pygmy Rice Rat has a wide distribution and presumably large overall population, and it occurs in protected areas in Bolivia, Paraguay, and north-western Argentina.   Bibliography.Anderson (1997), Bonvicino & Weksler (1998), Caceres et al. (2011), Contreras & Berry (1983), Gonzélez-Ittig, Rivera et al. (2014), Gonzélez-Ittig, Salazar-Bravo et al. (2010), Gonzalez-Ittig, Theiler & Gardenal (2002), Jayat, Ortiz & Miotti (2008), Malygin & Rosmiarek (2005), Mares, Braun & Gettinger (1989), Marinho-Filho et al. (2002), Myers & Carleton (1981), Olds & Anderson (1987), Pardinas, Teta et al. (2005), Rivera et al. (2007), de la Sancha (2014), Teta & Pardinas (2010), Weksler & Bonvicino (2005, 2015b), Weksler, Bonvicino, Pardinas et al. (2016), Yahnke (2006), Yensen et al. (1994). 3818814664 157 436 3818814821 157 436