Gray rice rat, Marañon oryzomys

Eremoryzomys polius

Eremoryzomys polius, also known as the gray rice rat or the Marañon oryzomys, is a rodent species in the tribe Oryzomyini of the family Cricetidae. Discovered in 1912 and first described in 1913 by Wilfred Osgood, it was originally placed in Oryzomys and named Oryzomys polius. In 2006, a cladistic analysis found that it was not closely related to Oryzomys in the strict sense or to any other oryzomyine then known, so that it is now placed in its own genus, Eremoryzomys. The Brazilian genus Drymoreomys, named in 2011, is probably the closest relative of Eremoryzomys. Eremoryzomys has a limited distribution in the dry upper valley of the Marañón River in central Peru, but may yet contain more than one species.

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A large, long-tailed rice rat, with head and body length of 138 to 164 mm (5.4 to 6.5 in), E. polius has gray fur and short ears. There are well-developed ungual tufts of hair on the hindfeet. Females have eight mammae. The rostrum (front part of the skull) is long and robust and the braincase is rounded. The bony palate is relatively short. The IUCN assesses the conservation status of the species as "Data Deficient"; it is poorly known but may be threatened by habitat destruction.

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Eremoryzomys polius is a large, long-tailed rice rat that in color resembles some North American woodrats (Neotoma ). The fur is grayish above and lighter below, where the hairs are gray at the bases but white at the tips. The external ears (pinnae) are short and the tail is dark above and light below. The hindfeet have well-developed ungual tufts (patches of hair) along the plantar margins and between all of the digits, a character shared only with Sooretamys angouya among oryzomyines. The squamae, small structures resembling scales that cover the soles of the hindfeet in many oryzomyines, are well developed. The claw of the first digit extends nearly to the end of the first phalanx of the second toe and the claw of the fifth toe extends slightly beyond the first phalanx of the fourth toe. As in most oryzomyines, the female has eight mammae. Head and body length is 138 to 164 mm (5.4 to 6.5 in). In Osgood's original two specimens, an old female and an adult female, tail length is 188 and 180 mm (7.4 and 7.1 in), respectively; hindfoot length is 30 and 30 mm (1.2 and 1.2 in); and greatest skull length is 37 and 34.7 mm (1.46 and 1.37 in). E. polius has 12 thoracic, 7 or 8 lumbar, and 35 or 36 caudal vertebrae; the presence of 12 thoracic vertebrae is a putative synapomorphy of Oryzomyini.



Biogeographical realms

As far as now known, Eremoryzomys polius is confined to a small area in central Peru, at an altitude of 760 to 2,100 m (2,490 to 6,890 ft), but the species may range more widely. It occurs in forest in the dry lowlands of the upper parts of the basin of the Marañón River, east of the main mountain range of the Andes. The biogeographical pattern indicated by the relationship between Eremoryzomys and the Brazilian Drymoreomys is unusual. While there are some similar cases of relationships between Andean and Atlantic Forest animals, these involve inhabitants of humid forests in the Andes; Eremoryzomys, in contrast, lives in an arid area. Because E. polius is so poorly known, the 2008 IUCN Red List assesses it as "Data Deficient". It is threatened by habitat destruction for cattle pasture and is not known from any protected areas.

Eremoryzomys habitat map
Eremoryzomys habitat map


1. Eremoryzomys Wikipedia article -
2. Eremoryzomys on The IUCN Red List site -

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