Mérida rice rat
Encyclopedia
Nephelomys meridensis, also known as the Mérida Oryzomys, is a species of rodent
in the genus Nephelomys
of family Cricetidae
. It is found in cloud forest
in the Sierra Nevada de Mérida
of western Venezuela
at elevations from 1500 to 3250 m. It is solitary, nocturnal and terrestrial, and has a varied diet.
N. meridensis has thick fur, which is about 11 mm long at the back. The color of the upperparts is rufous, with brown on the head, and becomes lighter towards the sides. The coloration of the underparts, which is well demarcated from that of the upper parts, is greyish, with a pure white area at the chest. The very large ears are covered with thin dark hairs. The hand and feet, whitish in color, are sparsely haired. The tail is brown above and somewhat paler below, and is not well-furred. The incisive foramina
, openings in the palate
before the molars
, are short. In the holotype
, the head and body length is 139 millimetres (5.47 in), the tail length is 143 millimetres (5.63 in), the hindfoot length is 30.7 millimetres (1.21 in), the ear length is 21 millimetre (0.826771653543307 in), and the skull length is 34.5 millimetres (1.36 in).
It was first described in 1894 by Oldfield Thomas
, who named it Oryzomys meridensis and considered it to be close to O. albigularis (currently Nephelomys albigularis) and O. velutinus (currently included in Hylaeamys megacephalus). In the next two decades, various other species were described in the group of O. albigularis and O. meridensis, which were eventually, in 1944, all consolidated under O. albigularis by Philip Hershkovitz
. Because of differences in karyotype
and morphometrics
, it was reinstated as a species separate from both O. albigularis and the other Venezuelan member of the group, O. caracolus, in the 1990s. When the species of the O. albigularis group were reclassified into the new genus Nephelomys in 2006, it was retained as a species, now named Nephelomys meridensis. In Táchira
, populations with a different karyotype
occur, which may represent a different species.
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 Sierra Nevada de Mérida
Sierra Nevada de Mérida
The Sierra Nevada de Mérida is the highest mountain range in the largest massif in Venezuela, the Cordillera de Mérida, which in turn is part of the northern extent of the Cordillera de los Andes...
of western 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 1500 to 3250 m. It is solitary, nocturnal and terrestrial, and has a varied diet.
N. meridensis has thick fur, which is about 11 mm long at the back. The color of the upperparts is rufous, with brown on the head, and becomes lighter towards the sides. The coloration of the underparts, which is well demarcated from that of the upper parts, is greyish, with a pure white area at the chest. The very large ears are covered with thin dark hairs. The hand and feet, whitish in color, are sparsely haired. The tail is brown above and somewhat paler below, and is not well-furred. The incisive foramina
Incisive foramen
The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...
, openings in 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...
before the molars
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
, are short. In the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, the head and body length is 139 millimetres (5.47 in), the tail length is 143 millimetres (5.63 in), the hindfoot length is 30.7 millimetres (1.21 in), the ear length is 21 millimetre (0.826771653543307 in), and the skull length is 34.5 millimetres (1.36 in).
It was first described in 1894 by 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...
, who named it Oryzomys meridensis and considered it to be close to O. albigularis (currently Nephelomys albigularis) and O. velutinus (currently included in Hylaeamys megacephalus). In the next two decades, various other species were described in the group of O. albigularis and O. meridensis, which were eventually, in 1944, all consolidated under O. albigularis by Philip Hershkovitz
Philip Hershkovitz
Philip Hershkovitz was an American mammalogist. Born in Pittsburgh, he attended the Universities of Pittsburgh and Michigan and lived in South America collecting mammals. In 1947, he was appointed a curator at the Field Museum of Natural History in Chicago and he continued to work there until his...
. Because of differences in 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...
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...
, it was reinstated as a species separate from both O. albigularis and the other Venezuelan member of the group, O. caracolus, in the 1990s. When the species of the O. albigularis group were reclassified into the new genus Nephelomys in 2006, it was retained as a species, now named Nephelomys meridensis. In Táchira
Táchira (state)
Táchira State is one of the 23 states of Venezuela. The state capital is San Cristóbal.Táchira State covers a total surface area of 11,100 km² and, in 2007, had an estimated population of 1,177,300....
, populations with a different 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...
occur, which may represent a different species.
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 29, 2009.
- Hershkovitz, P. 1944. A systematic review of the Neotropical water rats of the genus Nectomys (Cricetinae). Miscellaneous Publications Museum of Zoology, University of Michigan 58: 1–88.
- Thomas, O. 1894. Descriptions of some new Neotropical Muridae. Annals and Magazine of Natural History (6)14:346–365.
- Weksler, M., A. R. Percequillo, and R.S. Voss. 2006. Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae). American Museum Novitates 3537:1–29.