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Irenomys
''Irenomys tarsalis'', also known as the Chilean climbing mouse,〔 Chilean tree mouse,〔 or long-footed irenomys,〔Musser and Carleton, 2005, p. 1121〕 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.
''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).
==Taxonomy==
In 1900, Rodolfo Armando Philippi named both ''Mus tarsalis'' (from Valdivia Province in mainland Chile) and ''Reithrodon longicaudatus'' (from a small island near Chiloé),〔 both of which are now classified as ''Irenomys tarsalis''.〔Kelt, 1993, p. 1〕 Philippi's ''Reithrodon longicaudatus'' was transferred into a new genus, ''Irenomys'', by Oldfield Thomas in February 1919. The name, which means "peace mouse" in Greek, referred to the end of World War I four months before.〔Thomas, 1919, p. 201〕 Another of the species Philippi described in 1900, ''Mus mochae'', was later transferred to ''Irenomys'' because of a mismatch between the skin and skull,〔Osgood, 1943, pp. 171–172〕 but it is in fact a member of the genus ''Abrothrix'' and not closely related to ''Irenomys''.〔Musser and Carleton, 2005, p. 1090〕 In his 1943 work on ''The mammals of Chile'', Wilfred Hudson Osgood recognized the close relation between Philippi's ''Mus tarsalis'' and ''Reithrodon longicaudatus'' and referred them to a single species, then called ''Irenomys tarsalis''.〔Osgood, 1943, p. 219〕 Osgood retained two subspecies, ''Irenomys tarsalis tarsalis'' on the mainland and ''Irenomys tarsalis longicaudatus'' on Chiloé and nearby islands, on the basis of slight differences in pelage coloration. In the few mature specimens of the latter subspecies that Osgood had, the underparts are somewhat lighter than in examples of ''I. t. tarsalis'', which has a pinkish color in the underparts, but Osgood stressed that further material could well indicate that the two forms could not be distinguished.〔Osgood, 1943, p. 220〕
In his description of the genus, Thomas opined that ''Irenomys'' is most closely related to ''Phyllotis''.〔 The group of genera related to ''Phyllotis'' was later formalized as the tribe Phyllotini, and ''Irenomys'' was often included there, but also excluded from it by some authors.〔Steppan, 1995, pp. 6–7〕 In 1995, a cladistic analysis of Phyllotini on the basis of morphology provided evidence in favor of placement of ''Irenomys'' in the group, with some support for a close relation to ''Andinomys''.〔Steppan, 1995, figs. 22–24〕 From 1999 on, DNA sequence data cast doubt on this assignment, as studies using the mitochondrial cytochrome ''b'' gene and the nuclear IRBP gene placed ''Irenomys'' in a variety of positions, all outside Phyllotini, with ''Scolomys'', ''Sigmodon'', ''Euneomys'', and various large clades of sigmodontines all as sister groups in some analyses.〔Smith and Patton, 1999; D'Elía et al., 2003; D'Elía, 2003; D'Elía et al., 2006〕 Accordingly, it is now classified outside Phyllotini and considered as Sigmodontinae ''incertae sedis''.〔
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