''Nephelomys'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

oryzomyine Oryzomyini is a tribe (taxonomy), tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern List of mammals of the Uni ...

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

s found in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

from

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

, with a westward extension into the mountains of

Costa Rica Costa Rica (, ; ; literally "Rich Coast"), officially the Republic of Costa Rica ( es, República de Costa Rica), is a country in the Central American region of North America, bordered by Nicaragua to the north, the Caribbean Sea to the no ...

. Its generic name is derived from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

word ''nephelê'' "mist", referring to the

cloud forest A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest (TMCF), is a generally tropical or subtropical, evergreen, montane, moist forest characterized by a persistent, frequent or seasonal low-level cloud c ...

habitat of the members of the genus. The species in this genus have historically been placed in ''

Oryzomys ''Oryzomys'' is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat (''O. palustris'') of the United States and ...

'', but in 2006, Brazilian zoologist Marcelo Weksler and coworkers described it as a separate genus, because it is not closely related to the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

of ''Oryzomys''.Weksler, 2006 They are most closely related to other members of clade B, including ''

Euryoryzomys ''Euryoryzomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes six species, which are distributed in South America. Until 2006, its members were included in the genus ''Oryzomys'', but they are not closely related ...

'', ''

Transandinomys ''Transandinomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes two species—'' T. bolivaris'' and '' T. talamancae''—found in forests from Honduras in Central America south and east to southwester ...

'', ''

Hylaeamys ''Hylaeamys'' is a genus of South American oryzomyine rodents found principally in humid forested areas east of the Andes. The species in this genus have historically been placed in ''Oryzomys''. They are most closely related to ''Euryoryzomys'', ...

'', ''

Oecomys ''Oecomys'' is a genus of rodent within the tribe Oryzomyini of family Cricetidae. It contains about 17 species, which live in trees and are distributed across forested parts of South America, extending into Panama and Trinidad Trinidad i ...

'', and ''

Handleyomys ''Handleyomys'' is a genus of Central and South American rodents in the tribe Oryzomyini of family Cricetidae. It was first described in 2002 to include two species from the Colombian Andes which were previously included in distinct and unrelat ...

'', with some weak evidence supporting a sister-group relationship to ''Transandinomys''.Weksler et al., 2006, p. 20 ''Oryzomys'' appears in a different part of the oryzomyine

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rapid ...

, perhaps close to ''

Holochilus ''Holochilus'' is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae,* sometimes called marsh rats. It contains five living species, '' H. brasiliensis'', '' H. chacarius'', '' H. nanus'', '' H. oxe'', and '' H. sciureus' ...

'' and related genera. ''Nephelomys'' species have yellowish- to reddish-brown upperparts, and they are variable in the coloration of the underparts, with some possessing light, nearly white,

fur Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...

, which is separated from the color of the upperparts by an abrupt change in color, but others having ochraceous coloring which changes more gradually from the coloring on the back. Small patches of pure white fur may also be present on the underparts in some species. The ears are small, but the tail is long, and it is bicolored to a smaller or greater extent, depending on the species. Several

pads Pads (also called leg guards) are a type of protective equipment used in a number of sports and serve to protect the legs from the impact of a hard ball, puck, or other object of play travelling at high speed which could otherwise cause injuries t ...

are prominently present. Weksler and coworkers provided detailed comparisons among ''Euryoryzomys'', ''Hylaeamys'', ''Nephelomys'', and ''Transandinomys''. Among those genera, ''Nephelomys'' is unique in its short ears; in the relatively long claw on the fifth digit of the hindfoot; and in that the anterocone, the major cusp located at the front of the upper first molar, is divided into two smaller cusps. The divided anterocone appears to be a

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of the genus.Weksler et al., 2006, p. 21 Additionally, ''Nephelomys'' species are larger than those in ''Transandinomys'' and they have additional roots on the lower first molar that ''Transandinomys'' species lack. In 1961, all current ''Nephelomys'' species were classified under the single species ''Oryzomys albigularis'', but subsequently, the distinctiveness of various others was recognized. In 2005, seven species were listed under the ''O. albigularis'' group.Musser and Carleton, 2005, p. 1144 When ''Nephelomys'' was described as a separate species in 2006, six former

synonyms A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

were accorded specific status, so that a total of thirteen species are now recognized as valid.Weksler et al., 2006, p. 18

References

Literature cited

*Bangs, O. 1902. Chiriqui Mammalia. ''Bulletin of the Museum of Comparative Zoology'' 39:15–52. *Musser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.)
''Mammal Species of the World: a taxonomic and geographic reference''. 3rd ed
Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. *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. {{Taxonbar, from=Q305160 Taxa named by Marcelo Weksler Taxa named by Alexandre Reis Percequillo