Eremoryzomys

The first two specimens of Eremoryzomys polius were collected by Wilfred Osgood and M.P. Anderson in 1912. The next year, Osgood described these animals as a new species in the genus Oryzomys, Oryzomys polius. Osgood wrote that he was unable to find any species closely related to O. polius and compared it with O. xanthaeolus (currently Aegialomys xanthaeolus) "for convenience". Its relationships remained obscure ever afterward and it was never assigned to any of the several groups of species recognized within Oryzomys. In 2006, Marcelo Weksler published a large-scale cladistic analysis of Oryzomyini ("rice rats"), the tribe to which O. polius belongs. He used both morphological data and molecular characters from the IRBP gene. In all of his analyses, O. polius was found to be part of clade D, one of four large groups within Oryzomyini, as the sister group to a clade containing all the other species of clade D. Clade D was supported by two shared derived (synapomorphic) molecular characters and by seven morphological synapomorphies—the tail has a different color above and below; the parietal bone extends to the side of the skull; the incisive foramina (openings in the palate) extend back between the first molars; the posterolateral palatal pits (perforations of the palate near the third molars) are complex; the sphenopalatine vacuities (openings in the mesopterygoid fossa, the gap behind the end of the palate) are large; the pattern of the arterial circulation in the head is derived; and the posteroloph (a crest at the back) is present on the third upper molar. Two other molecular synapomorphies supported the clade of all members of clade D except O. polius, coupled with three morphological traits—in these species, but not in O. polius, the first upper molar has an additional small root at the outer (labial) side; the first lower molar has additional small roots; and the second upper molar has the mesoflexus (one of the valleys between the cusps and crests) divided in two. In Weksler's analysis, species placed in Oryzomys did not form a coherent (monophyletic) group, but instead were found at various positions across the oryzomyine tree, and he suggested that most of these species, including O. polius, should be placed in new genera. Later in 2006, Weksler and others described ten new genera for species formerly placed in Oryzomys, including Eremoryzomys for polius; thus, the species is now known as Eremoryzomys polius. In reference to its "isolated distribution", they incorporated the Greek word eremia "lonely place" into the generic name. The 2008 IUCN Red List, citing Pacheco, commented that Eremoryzomys may in fact include more than one species. Eremoryzomys is now one of about 28 genera ==Description==

Eremoryzomys polius is a large, long-tailed rice rat that in color resembles some North American woodrats (Neotoma). 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. Head and body length is . In Osgood's original two specimens, an old female and an adult female, tail length is , respectively; hindfoot length is ; and greatest skull length is . the presence of 12 thoracic vertebrae is a putative synapomorphy of Oryzomyini. Skull . The zygomatic notch, an extension at the front of the zygomatic plate, is present. The plate's back margin is level with the front of the first upper molar. The narrowest part of the interorbital region (located between the eyes) is to the front and the region's margins exhibit strong beading. Various crests develop on the rounded braincase, especially in old animals. The interparietal bone at the back of the braincase is narrow and wedge-shaped, so that the parietal and occipital bones meet extensively. The incisive foramina are very long, extending well between the molars. The posterolateral palatal pits are well-developed and recessed into a fossa (depression). The squamosal lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity, a defining character of oryzomyines. In the mandible, the mental foramen, an opening in the mandible just before the first molar, opens to the outside, not upwards as in a few other oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, usually join into a single crest at a point below the first molar and do not extend forward beyond the molar. There is no distinct capsular process of the lower incisor, a trait Eremoryzomys shares with only a few other oryzomyines. Molars The molars are bunodont (with the cusps higher than the connecting crests) and brachydont (low-crowned). On the upper first and second molar, the outer and inner valleys between the cusps and crests do not interpenetrate. Many accessory crests are present, including the mesolophs and mesolophids. The anterocone and anteroconid, the front cusps on the upper and lower first molar, are not divided into smaller outer and inner cusps. ==Distribution and status==

As far as now known, Eremoryzomys polius is confined to a small area in central Peru, at an altitude of , 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. ==Notes==

• • Osgood, W.H. 1913. New Peruvian mammals. Field Museum of Natural History, Zoölogical Series 10:93–100. • • • Weksler, M. 2006. Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data. Bulletin of the American Museum of Natural History 296:1–149. • Weksler, M., Percequillo, A.R. and Voss, R.S. 2006. Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae). American Museum Novitates 3537:1–29.