The Sigmodontinae is one of the most diverse groups of mammals. It includes at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count numbers at least 508. They are distributed throughout the New World, but are predominantly South American. The sigmodontines inhabit many of the same ecological niches that the Murinae inhabit in the Old World.
Akodontini is the second most speciose tribe of the subfamily Sigmodontinae. It includes at least 106 living species in 19 genera and is distributed mainly in the southern half of South America, with only two genera extending into Guyana and Venezuela. It also includes genera previously placed in tribe Scapteromyini.
Philip Myers' Akodont (Akodon philipmyersi) is a recently described species of grass mouse from Misiones Province, Argentina. Like other grass mice, A. philipmyersi is a small, non-descript, greyish-brown mouse with prominent ears. The species was recognized as distinct from other grass mice on the basis of unique features of karyology, genetic sequence, cranial measurements, and general morphology.
Akodon is a genus consisting of South American grass mice. Grass mice are found throughout South America, but the genus is absent from the Amazon lowlands, west of the southern Andes, and from extreme southern South America. Akodon is one of the most species-rich genera of Neotropical rodents. Species of Akodon are known to inhabit a variety of habitats from tropical and tropical moist forests to altiplano and desert. Akodon is the largest genus in the tribe Akodontini.
Bibimys is a genus of new world rats. Commonly known as the crimson-nosed rats, there are three species: Bibimys chacoensis - Chaco Crimson-nosed Rat - found in north-east Argentina Bibimys labiosus - Large-lipped Crimson-nosed Rat - south-east Brazil Bibimys torresi - Torres' Crimson-nosed Rat - central Argentina Presently, the distributional range of Bibimys covers Argentina, Brasil and Paraguay.