Nephelomys caracolus, also known as the Costa Central Oryzomys or Caracol Rice Rat, is a species of 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....

 in the genus Nephelomys

Nephelomys

Nephelomys is a genus of South American oryzomyine rodents found in the Andes from Bolivia to Venezuela, with a westward extension into the mountains of Costa Rica...

of family Cricetidae

Cricetidae

The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...

. It is found in 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...

 in the Cordillera de la Costa Central

Cordillera de la Costa Central

The Cordillera de la Costa Central is a range of mountains in Venezuela, which run east to west along the country's northern coast. It is also known as the Central Range.In the east they follow the border between the states of Vargas and Miranda...

 of Aragua

Aragua (state)

Aragua State is located in the north-central region of Venezuela. It has plains and jungles and Caribbean beaches. The most popular are Cata and Choroni...

, Miranda

Miranda (state)

Miranda State is one of the 23 states into which Venezuela is divided. It is ranked second in population among Venezuelan states, after Zulia State. In June 30, 2010, it had approximately 2,987,968 residents. It also has the greatest Human Development Index in Venezuela, according to the...

, and the Distrito Federal

Venezuelan Capital District

The Capital District of Venezuela is a federal district corresponding to the capital Caracas. It has an area of 433 km² and there is only one administrative division , Libertador, which contains about half City of Caracas. It is the seat of the federal government and the head of the public...

 in north-central 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...

 at elevations from 1000 to 2500 m. It is nocturnal and terrestrial, and has a varied diet. In most Nephelomys species, the posterolateral palatal pits

Posterolateral palatal pits

In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars. Posterolateral palatal pits are present, in various degrees of development, in several members of the rodent family Cricetidae...

, perforations of the palate

Palate

The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...

 near the third molar, are conspicuous and receded into a fossa

Fossa (anatomy)

In anatomical terminology, fossa has come to mean a depression or hollow, in general, in a bone. Other parts of the body may be involved, for example, the antecubital fossa...

, but in N. caracolus and the Ecuadorian species N. nimbosus

Nephelomys nimbosus

Nephelomys nimbosus is a species of rodent in the genus Nephelomys of family Cricetidae. Its type locality is at San Antonio on the northeastern slope of the Tungurahua in the Andes of Ecuador, at an altitude of about . The type series included five individuals.The fur of the upperparts is brown to...

, the pits are much smaller.

Oldfield Thomas

Oldfield Thomas

Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...

 originally described the species, in 1914, as a member of 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...

, Oryzomys caracolus. From 1960 on, it was included in Oryzomys capito, the current Hylaeamys megacephalus, and subsequently in Oryzomys albigularis. In the 1990s, studies of the Venezuelan populations of the O. albigularis group, based on data from karyotype

Karyotype

A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...

s and morphometrics

Morphometrics

Morphometrics refers to the quantitative analysis of form, a concept that encompasses size and shape. Morphometric analyses are commonly performed on organisms, and are useful in analyzing their fossil record, the impact of mutations on shape, developmental changes in form, covariances between...

, provided evidence for the distinctiveness of O. caracolus and the other Venezuelan species of the group, O. meridensis. The patterns recovered differ in details among the studies, however, and some authors chose to retain O. caracolus and O. meridensis as subspecies

Subspecies

Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...

of O. albigularis, suggesting a need for further study on the classification of Venezuelan members of the group. When the members of the O. albigularis group were transferred to the new genus Nephelomys in 2006, caracolus was retained as a species, Nephelomys caracolus.

Literature cited

• Aguilera, M., Ochoa, J., Weksler, M. and Rivas, B. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.1. www.iucnredlist.org Retrieved on June 28, 2009.
• Weksler, M., A. R. Percequillo, and R.S. Voss. 2006. Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae). American Museum Novitates 3537:1–29.