Octomys mimax Thomas 1920
Creators: name: Don E. Wilson
name: Thomas E. Lacher, Jr
name: Russell A. Mittermeier
Publisher: name: Lynx Edicions
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Octodontidae
Octomys
Octomys mimax

description: 5.
Common Viscacha Rat
Octomys mimax
French: Octodon vizcacha / German: Viscacharatte / Spanish: Rata vizcacha del Monte
Other common names: Mountain Viscacha Rat, Viscacha Rat
Taxonomy. Octomys mimax Thomas, 1920,
“La Puntilla, near Tinogasta...a few miles | out from Tinogasta toward Copacabana, at an altitude of about 1000 metres,” Catamarca Province, Argentina.
No fossils of O. mimax are known. Monotypic.
Distribution. W Argentina, in Catamarca, La Rioja, San Juan, San Luis, and Mendoza provinces.
Descriptive notes. Head-body 140-330 mm,tail 105-179 mm, ear 21-4-27-4 mm, hindfoot 32:3-36-6 mm; weight averaging 95-8 g. No sexual dimorphism in body weight. The Common Viscacha Rat is mediumsized. Skull is long and slender, with large and well-developed tympanic bullae butless developed than in species of Tympanoctomys. Dorsal fur is light brown and venteris white. Tail is long (c.50% ofits total length), bicolored, and hairy, with conspicuous terminal tuft. Oral vibrissae are present, but function is unknown. Chromosome complement is 2n = 56, FN = 108. Karyotype is composed of five small submetacentric chromosomes, 21 small metacentric chromosomes, and one small subtelocentric chromosome. Xand Y-chromosomes are a small subtelocentric and medium-sized metacentric, respectively.
Habitat. [Lowland deserts with abundant rocks, foothills, low scrub areas, ravines, and gorges at elevations up to 800 m. The Common Viscacha Ratis a saxicolous and surface-dwelling rodent; it is a habitat specialist that lives and constructs burrows in rock formations. It also occurs in rocky macrohabitats with creosote bush (Larrea, Zygophyllaceae), “chical” (rocky substrate dominated by Ramorinoa girolae, Fabaceae, a species endemic to the temperate Monte Desert), and columnar cactus slopes.
Food and Feeding. The Common Viscacha Ratis strictly herbivorous. Diets are mainly leaves of shrubs and trees but include cacti throughout the year and seeds and fruits, principally Prosopis (Fabaceae), in the wet season. They also include Larrea, cacti, species of Amaranthaceae, and drupe-type fruits (e.g. Lycium, Solanaceae) from which it may obtain preformed water. Diet also includes seedsrich in carbohydrates, a potential source of metabolic water (e.g. Prosopis).
Breeding. Most observations regarding breeding of Common Viscacha Rats are anecdotal from captured young individuals in the same trap in November at Valle de la Luna, San Juan Province; they suggest that breeding occurs at the end of winter (August) or beginning of spring (September).
Activity patterns. Common Viscacha Rats are nocturnal and most active after sunset; activity decreases substantially after sunrise. They are good thermoregulators, enabling nocturnal activity. Ambient temperatures can drop below freezing at nightin the Monte Desert. Individuals use rock crevices for refuge and resting sites because they provide thermally stable environments (especially in summer).
Movements, Home range and Social organization. The Common Viscacha Rat ranges over large areas and exhibits low spatial overlap; overlap among conspecificsis similar for both sexes. Average home ranges (males and females combined) are 12,370 m? however, male Common Viscacha Rats have larger home ranges than females. Common Viscacha Rats are solitary and do not share resting sites during the day.
Status and Conservation. Classified as a Least Concern on The IUCN Red List. Updated information on status of populations of the Common Viscacha Rat is needed, and if current agricultural trends persist, it may qualify for a Near Threatened status. It was considered as Vulnerable in a regional IUCN assessment of threatened mammals in Argentina.
Bibliography. Berman (2003), Bozinovic & Contreras (1990), Campos & Giannoni (2013), Campos, Andino et al. (2013), Campos, Giannoni et al. (2015), Contreras et al. (1994), Ebensperger et al. (2008), Gallardo (1992), Gallardo et al. (2007), Mares (1980), Mares et al. (2000), Ojeda, A.A. et al. (2013), Ojeda, R.A. & Bidau (2013f), Ojeda, R.A., Borghi & Roig (2002), Ojeda, R.A., Gonnet et al. (1996), Oyarce et al. (2003), Redford & Eisenberg (1992), Sobrero et al. (2010), Woods & Kilpatrick (2005).
description: Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Octodontidae, pp. 536-541 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on page 539, DOI: 10.5281/zenodo.6615351