The mountain viscacha rat or mountain vizcacha rat (''Octomys mimax''), historically viscacha rat or vizcacha rat, is a species of
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 ...
in the family
Octodontidae
Octodontidae is a family of rodents, restricted to southwestern South America. Fourteen species of octodontid are recognised, arranged in seven genera. The best known species is the common degu, ''Octodon degus''.
Octodontids are medium-sized ...
.
It is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
.
It is the only living species within the genus ''Octomys''.
[ This ]diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
genus (2n = 56) may be ancestral to the two unusual suspected tetraploid
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...
species ''Tympanoctomys barrerae
The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat (''Tympanoctomys barrerae'') is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus ''Tympanoctomys''.
Des ...
'' and ''Pipanacoctomys aureus
The golden viscacha rat or golden vizcacha rat (''Pipanacoctomys aureus'') is the single species of the genus ''Pipanacoctomys'' of the rodent family Octodontidae. It has 92 chromosomes and has been regarded as tetraploid ( 4x = 2n).Gallardo, M. ...
''. However, some genetic studies have rejected any polyploidism in mammals as unlikely, and suggests that ''amplification and dispersion of repetitive sequences best explain the large genome size''.
Description
The mountain viscacha rat is a rat-like animal with a head-body length of about and weighing from . The feet are relatively long, while the tail measures . It has light brown fur with white underparts and a bushy tail.[ ]
Unusual features of the viscacha rat include greatly enlarged auditory bulla
The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal.
It originates as a separate bone (tympanic ...
e, and the presence of numerous whisker
Vibrissae (; singular: vibrissa; ), more generally called Whiskers, are a type of stiff, functional hair used by mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser ...
s on the roof of the mouth behind the incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...
teeth. The exact function of the whiskers is unclear, but they may enable the animal to sense the position of food inside the mouth.
Distribution and habitat
Mountain viscacha rats are found only in the Monte Desert
The Monte Desert is a South American desert, lying entirely within Argentina and covering approximately the submontane areas of Catamarca, La Rioja, San Juan, San Luis and Mendoza Provinces, plus the western half of La Pampa Province and the e ...
region of northwestern Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
, specifically in the provinces of Catamarca, La Rioja
La Rioja () is an autonomous community and province in Spain, in the north of the Iberian Peninsula. Its capital is Logroño. Other cities and towns in the province include Calahorra, Arnedo, Alfaro, Haro, Santo Domingo de la Calzada, and Nà ...
, San Luis, San Juan. They inhabit rocky desert and semidesert environments up to above sea level.[
]
Behaviour
Mountain viscacha rats are nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
and solitary, spending the day sheltering in rock crevices. Although it does not construct burrows, it may place pieces of cactus
A cactus (, or less commonly, cactus) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word ''cactus'' derives, through Latin, from the Ancient Greek ...
close to crevice entrances to help protect against predators.[ Individuals occupy large home ranges of around , often overlapping with those of their neighbours.] They are herbivorous, feeding on the leaves and seeds of shrubland vegetation. During the dry season, their diet consists largely of the leaves of ''Prosopis
''Prosopis'' is a genus of flowering plants in the family Fabaceae. It contains around 45 species of spiny trees and shrubs found in subtropical and tropical regions of the Americas, Africa, Western Asia, and South Asia. They often thrive in ari ...
'' trees, supplemented by caperbushes and alkaliweeds. During the wet season, they eat more seeds and fruit, including those from plants such as ''Maytenus
''Maytenus'' ''Sunset Western Garden Book,'' 1995:606–607 is a genus of flowering plants in the family Celastraceae. Members of the genus are distributed throughout Central and South America, Southeast Asia, Micronesia and Australasia, the Indi ...
'' and boxthorn
''Lycium'' is a genus of flowering plants in the nightshade family, Solanaceae. The genus has a disjunct distribution around the globe, with species occurring on most continents in temperate and subtropical regions. South America has the most ...
shrubs.[
]
References
External links
*
*Mares, M. A.; Braun, J. K.; Barquez, R. M.; DÃaz, M. M. 2000
Two new genera and species of halophytic desert mammals from isolated salt flats in Argentina
Occasional Papers, Museum of Texas Tech University 203:i+1-27.
*
{{Taxonbar, from=Q631698
Octodontidae
Mammals of Chile
Mammals of Argentina
Mammals described in 1920
Taxa named by Oldfield Thomas
Taxonomy articles created by Polbot
High Monte