Nephelomys
Encyclopedia
Nephelomys is a genus
of South America
n oryzomyine
rodent
s found in the Andes
from Bolivia
to Venezuela
, with a westward extension into the mountains of Costa Rica
. Its generic name is derived from the Ancient Greek
word nephelê "mist", referring to the cloud forest
habitat of the members of the genus.
The species in this genus have historically been placed in Oryzomys
, 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
of Oryzomys. They are most closely related to other members of clade B, including Euryoryzomys
, Transandinomys
, Hylaeamys
, Oecomys
, and Handleyomys
, with some weak evidence supporting a sister-group relationship to Transandinomys. Oryzomys appears in a different part of the oryzomyine evolutionary radiation
, perhaps close to Holochilus
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
, 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 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
of the genus. 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. When Nephelomys was described as a separate species in 2006, six former synonyms
were accorded specific status, so that a total of thirteen species are now recognized as valid.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
n oryzomyine
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands...
rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s found in the Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
from Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
to Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
, with a westward extension into the mountains of Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
. Its generic name is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
word nephelê "mist", referring to the cloud forest
Cloud forest
A cloud forest, also called a fog forest, is a generally tropical or subtropical evergreen montane moist forest characterized by a persistent, frequent or seasonal low-level cloud cover, usually at the canopy level. Cloud forests often exhibit an abundance of mosses covering the ground and...
habitat of the members of the genus.
The species in this genus have historically been placed in Oryzomys
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 of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...
, 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
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of Oryzomys. They are most closely related to other members of clade B, including Euryoryzomys
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 to the type species of that genus, and therefore they were...
, Transandinomys
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 southwestern Ecuador and northwestern Venezuela in northern South America...
, Hylaeamys
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, Transandinomys, Nephelomys, Oecomys, and Handleyomys, and most...
, Oecomys
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.-Literature cited:...
, and Handleyomys
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 unrelated genera, Aepeomys and Oryzomys, but which turned out to...
, with some weak evidence supporting a sister-group relationship to Transandinomys. Oryzomys appears in a different part of the oryzomyine evolutionary radiation
Evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...
, perhaps close to Holochilus
Holochilus
Holochilus is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae, sometimes called marsh rats. It contains three living species, Holochilus brasiliensis, Holochilus chacarius, and Holochilus sciureus, which are widely distributed in South America east of the Andes, and a...
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
Fur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...
, 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 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
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
of the genus. 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. When Nephelomys was described as a separate species in 2006, six former synonyms
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
were accorded specific status, so that a total of thirteen species are now recognized as valid.
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. ISBN 978-0-8018-8221-0
- 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.