Irenomys tarsalis

Irenomys tarsalis, also known as the Chilean climbing mouse, Chilean tree mouse, or long-footed irenomys, is a rodent found in Chile, from about 36° to 46°S, and in adjacent Argentina, mainly in forests. It is a large, long-tailed, soft-furred mouse characterized by grooved upper incisors and specialized molars with transverse ridges, divided by deep valleys, which are connected by a transverse ridge along the midline of the molars.

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I. tarsalis is a docile, herbivorous animal that lives in trees. It is so distinct from other species that it was placed in its own genus, Irenomys, in 1919. The name comes from the Ancient Greek word εἰρήνη (iren ) meaning "peace", in reference to the end of World War I. Although it has been generally placed in the tribe Phyllotini, genetic evidence does not support any close relationships with other genera, so that it is now classified as a member of the subfamily Sigmodontinae incertae sedis (of uncertain position).

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Irenomys is a large mouse with a long, hairy tail, large eyes, and long and soft fur. The upperparts are rufous with fine dark lines and the underparts are buff, with the exact color varying by subspecies. The densely haired ears are medium-sized and blackish in color. The feet, which are large and broad, are nearly white. The tail, which ends in a slight pencil, is dark brown, with a somewhat lighter area present on the ventral side in some individuals. The total length is 270 to 326 millimetres (10.63 to 12.83 in), averaging 280 millimetres (11.02 in), the tail length is 162 to 196 millimetres (6.38 to 7.72 in), averaging 165 millimetres (6.50 in), the hindfoot length is 28 to 32 millimetres (1.10 to 1.26 in), averaging 30 millimetres (1.18 in), the ear length is 20 to 25 millimetres (0.79 to 0.98 in), averaging 22 millimetres (0.87 in), and weight is 40 to 59 grams (1.4 to 2.1 oz), averaging 42 grams (1.5 oz). The karyotype includes 64 chromosomes, with a fundamental number (FN) of 98.

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The skull resembles that of some Rhipidomys species. The interorbital region is narrow and the incisive foramina are long, extending between the first molars. The upper incisors are deeply grooved. The molars are strongly hypsodont (high-crowned) and consist of transverse, diamond-shaped laminae (plates), separated by deep valleys, which are joined at the midline by narrow ridges, similar to those of the African elephant.

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Biogeographical realms

Habits and Lifestyle

Irenomys tarsalis is restricted to forested habitats in Chile and western Argentina. In the northern part of its range, its distribution falls into two segments, one in coastal Chile and one further east in Chile and in adjacent Argentina, both of which extend north to about 36°S. Further south, it also occurs in Chile and adjacent Argentina, and also on numerous Chilean islands, including Chiloé. The southernmost records are at about 46°S. No fossils are known. It generally occurs in humid and densely forested habitats, often with bamboo vegetations, but a specimen has been reported from riparian vegetation at a small stream near the southern limit of its distribution and it is also found in unforested steppe habitat with scattered Austrocedrus chilensis trees. It does not occur on high elevations. It was a common species during a population peak of small rodents evidently caused by the flowering of quila (Chusquea quila ) bamboo.

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It is found in association with other rodents such as Abrothrix olivaceus, Abrothrix longipilis, Oligoryzomys longicaudatus, Geoxus valdivianus, and Auliscomys pictus, as well as the marsupials Rhyncholestes raphanurus and Dromiciops gliroides. Remains of Irenomys have been found in owl pellets of the great horned owl (Bubo virginianus ), rufous-legged owl (Strix rufipes ), and barn owl (Tyto alba ); other potential predators include another owl, the Austral pygmy-owl (Glaucidium nanum ), and the South American gray fox (Pseudalopex griseus ), Darwin's fox (Pseudalopex fulvipes ) and Kodkod (Leopardus guigna ).

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Population number

Irenomys is not currently threatened and it is classified as "least concern" by the International Union for Conservation of Nature. It occurs in several protected areas, but destruction of its forest habitat may pose a threat to some populations.


1. Irenomys Wikipedia article -
2. Irenomys on The IUCN Red List site -

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