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 (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

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 only 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 foun ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. 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. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

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 two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

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''. 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 b ...

e, and the presence of numerous

whisker Whiskers, also known as vibrissae (; vibrissa; ) are a type of stiff, functional hair used by most therian mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser as t ...

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, wher ...

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 ext ...

region of northwestern

, specifically in the provinces of Catamarca,

La Rioja La Rioja () is an autonomous communities in Spain, autonomous community and provinces of Spain, province in Spain, in the north of the Iberian Peninsula. Its capital is Logroño. Other List of municipalities in La Rioja, cities and towns in the ...

, San Luis,

San Juan San Juan, Spanish for Saint John (disambiguation), Saint John, most commonly refers to: * San Juan, Puerto Rico * San Juan, Argentina * San Juan, Metro Manila, a highly urbanized city in the Philippines San Juan may also refer to: Places Arge ...

. They inhabit rocky desert and semidesert environments up to above sea level.

Behaviour

Mountain viscacha rats are

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

and solitary, spending the day sheltering in rock crevices. Although it does not construct burrows, it may place pieces of

cactus A cactus (: cacti, cactuses, or less commonly, cactus) is a member of the plant family Cactaceae (), a family of the order Caryophyllales comprising about 127 genera with some 1,750 known species. The word ''cactus'' derives, through Latin, ...

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. The current circumscription of the genus contains three species found in northern Africa, the Middle East, Central and South Asia. Previously it also contained around 40 species ...

'' trees, supplemented by caperbushes and alkaliweeds. During the wet season, they eat more seeds and fruit, including those from plants such as ''

Maytenus ''Maytenus'' is a genus of flowering plants in the family Celastraceae. Members of the genus are distributed throughout Central America, Central and South America, Southeast Asia, Micronesia, and Australasia, the Indian Ocean and Africa. They gr ...

'' 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 spec ...

shrubs.

References

External links

* *Mares, M. A.; Braun, J. K.; Barquez, R. M.; Díaz, 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=Q12264988 , from2=Q631698 Octodontidae Mammals of Argentina Endemic fauna of Argentina Mammals described in 1920 Taxa named by Oldfield Thomas Taxonomy articles created by Polbot High Monte