Evolution and systematics

The chinchilla rats, or chinchillones (genus Abrocoma), belong to the Abrocomidae family, in the order Rodentia. Within the genus Abrocoma, there are three species. The two best-studied are the ashy chinchilla rat (Abrocoma cinerea) and Bennett's chinchilla rat (Abrocoma bennettii). In 1990, a third species was designated, namely the Bolivian chinchilla rat (Abrocoma boliviensis). Another species, Abrocoma vaccarum, has been the subject of only a few academic reports and is considered a systematic development, rather than a true species.

In 1999, a new genus, Cuscomys, was described in the Peruvian Andes. As of 2003, two species are included in the genus. Of these, one (Cuscomys oblativa) is presumed to be extinct, and is represented only by remains discovered in burial sites in Peru. The other species is the Ashaninka rat, Cuscomys ashaninka. To date, only the recently-killed corpse of a single member of the species has been discovered. Until further specimens are recovered, information concerning Cuscomys is pending, and this species designation is not widely accepted.

The evolutionary history of the family Abrocomidae dates back to the Early Miocene Epoch (from 23.8 million to 16.4 million years ago), in what is present-day Argentina. Evolutionary diversification of the octodont rodents, which led to the development of the six families, including Abro-comidae, is thought to have had its genesis after the separation of the South American continent from other continental masses.

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