{{Short description|Species of rodent}} {{Hatnote|This species was historically called viscacha rat. See Viscacha rat for a list of other viscacha rats now considered distinct.}} {{Speciesbox | name = Mountain viscacha rat | image = | status = LC | status_system = IUCN3.1 | status_ref = <ref name="iucn status 11 November 2021">{{cite iucn |author=Roach, N. |date=2016 |title=''Octomys mimax'' |volume=2016 |article-number=e.T15093A78321632 |doi=10.2305/IUCN.UK.2016-2.RLTS.T15093A78321632.en |access-date=11 November 2021}}</ref> | genus = Octomys | parent_authority = Thomas, 1920 | species = mimax | authority = Thomas, 1920 }}

The '''mountain viscacha rat''' or '''mountain vizcacha rat''' ('''''Octomys mimax'''''), historically '''viscacha rat''' or '''vizcacha rat''', is a species of rodent in the family Octodontidae.<ref name = MSW3>{{MSW3 Hystricognathi | id = 13400379 | pages = 1572}}</ref> It is endemic to Argentina.<ref name="iucn status 11 November 2021" />

It is the only living species within the genus '''''Octomys'''''.<ref name=Sobrero2010/> This diploid genus (2n = 56) may be ancestral to the two unusual suspected tetraploid species ''Tympanoctomys barrerae'' and ''Pipanacoctomys aureus''.<ref name=Gallardo2006>{{cite journal | author = Gallardo, M.H. | year = 2006 | title = Molecular cytogenetics and allotetraploidy in the red vizcacha rat, ''Tympanoctomys barrerae'' (Rodentia, Octodontidae)] | journal = Genomics | volume =88 | issue = 2 | pages = 214–221 | doi = 10.1016/j.ygeno.2006.02.010 | pmid=16580173| doi-access = free | hdl = 10533/178085 | hdl-access = free }}</ref> 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''.<ref name="Svartman 2005">{{cite journal |doi=10.1016/j.ygeno.2004.12.004 |title=Molecular cytogenetics discards polyploidy in mammals |year=2005 |last1=Svartman |first1=Marta |last2=Stone |first2=Gary |last3=Stanyon |first3=Roscoe |journal=Genomics |volume=85 |issue=4 |pages=425–30 |pmid=15780745}}</ref>

==Description== The mountain viscacha rat is a rat-like animal with a head-body length of about {{convert|11|to|18|cm|in}} and weighing from {{convert|85|to|121|g|oz}}. The feet are relatively long, while the tail measures {{convert|12|to|16|cm|in}}. It has light brown fur with white underparts and a bushy tail.<ref name=Sobrero2010>{{cite journal | author = Sobrero, R.| year = 2010 | title = ''Octomys mimax'' (Rodentia: Octodontidae) | journal = Mammalian Species | volume = 42 | issue = 1 | pages = 49–57 | doi = 10.1644/853.1|display-authors=etal| doi-access = free }}</ref>

Unusual features of the viscacha rat include greatly enlarged auditory bullae, and the presence of numerous whiskers on the roof of the mouth behind the incisor teeth. The exact function of the whiskers is unclear, but they may enable the animal to sense the position of food inside the mouth.<ref name=Berman2003>{{cite journal | author = Berman, S.L. | year = 2003 | title = A desert octodontid rodent, ''Tympanoctomys barrerae'', uses modified hairs for stripping epidermal tissue from leaves of halophytic plants | journal = Journal of Morphology | volume = 257 | issue = 1 | pages = 53–61 | doi = 10.1002/jmor.10115| pmid = 12740896 | bibcode = 2003JMorp.257...53B | s2cid = 25765293 }}</ref>

==Distribution and habitat== Mountain viscacha rats are found only in the Monte Desert region of northwestern Argentina,<ref name="iucn status 11 November 2021" /> specifically in the provinces of Catamarca, La Rioja, San Luis, San Juan. They inhabit rocky desert and semidesert environments up to {{convert|800|m|ft}} above sea level.<ref name=Sobrero2010/>

==Behaviour== Mountain viscacha rats are nocturnal and solitary, spending the day sheltering in rock crevices. Although it does not construct burrows, it may place pieces of cactus close to crevice entrances to help protect against predators.<ref name=Sobrero2010/> Individuals occupy large home ranges of around {{convert|12300|m2|acre}}, often overlapping with those of their neighbours.<ref name=Ebensperger2008>{{cite journal | author = Ebensperger, L.A.| year = 2008 | title = Activity, range areas, and nesting patterns in the viscacha rat, ''Octomys mimax'' | journal = Journal of Arid Environments | volume = 72 | issue = 7 | pages = 1174–1183 | doi = 10.1016/j.jaridenv.2008.02.003| bibcode = 2008JArEn..72.1174E |display-authors=etal| hdl = 10533/237536 | hdl-access = free }}</ref> 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'' trees, supplemented by caperbushes and alkaliweeds. During the wet season, they eat more seeds and fruit, including those from plants such as ''Maytenus'' and boxthorn shrubs.<ref name=Sobrero2010/>

==References== {{Reflist}}

==External links== *{{Citation | doi = 10.1111/j.1095-8312.2004.00331.x | last1 = Gallardo | first1 = M.H. | last2 = Kausel | year = 2004 | first2 = G. | last3 = Jiménez | first3 = A. | last4 = Bacquet | first4 = C. | last5 = González | first5 = C. | last6 = Figueroa | first6 = J. | last7 = Köhler | first7 = N. | last8 = Ojeda | first8 = R. | title = Whole-genome duplications in South American desert rodents (Octodontidae) | journal = Biological Journal of the Linnean Society | volume = 82 | issue = 4 | pages = 443–451 | postscript = . | doi-access = free | hdl = 11336/102012 | hdl-access = free }} *Mares, M. A.; Braun, J. K.; Barquez, R. M.; Díaz, M. M. 2000. [https://web.archive.org/web/20120217181328/http://www.nsrl.ttu.edu/publications/opapers/ops/op203.pdf 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.

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Category:Octodontidae Category:Mammals of Argentina Category:Endemic fauna of Argentina Category:Mammals described in 1920 Category:Taxa named by Oldfield Thomas Category:Taxonomy articles created by Polbot Category:High Monte