Proechimys is a genus of South American spiny rats of the family Echimyidae. All species of the genus are terrestrial. In the lowland Neotropical forests, Proechimys rodents are often the most abundant non-volant mammals. They are recognizable by reason of their elongated heads and long rostra, large and erect ears, narrow and long hind feet, and tails always shorter than head-and-body lengths. The dorsal pelage comprises a mixture of expanded, varyingly stiffened spines (or aristiforms) — hence the vernacular name of spiny rats — and soft hairs (or setiforms). Proechimys is the most speciose genus of the rodent family Echimyidae, with 25 species recognized, followed by Phyllomys with 13 species, and Trinomys with 11 species.

Phylogeny

Genus level

The genus Proechimys is the sister group to the genus Hoplomys (the armored rat). In turn, these two taxa share evolutionary affinities with other Myocastorini genera: Callistomys (the painted tree-rat) and Myocastor (the coypu or nutria) on the one hand, and Thrichomys on the other hand.

Species level

Reconstructing the systematics and phylogeny of Proechimys species have been greatly hampered by extreme levels of within- and among-population character variability. This difficulty has been emphasized by Pine et al.: "Among the rodents, Proechimys remains what may be the most problematical genus taxonomically in all mammaldom." To infer the phylogeny of Proechimys at the species level, morphological characters and mitochondrial DNA sequences have been used, and allowed to group species into major clades but whose interrelationships remain unresolved. Six species groups were identified (group semispinosus, group longicaudatus, group guyannensis, group trinitatus, group goeldii, and group gardneri), and 4 species (Proechimys simonsi, P. echinothrix, P. canicollis, and P. decumanus) remained unaffiliated to any of these groups. The different groups of species can be diagnosed as follows.

Distribution

Proechimys species presently occur mainly in South America, in all countries except Argentina, Uruguay, and Chile. One member of the genus (P. semispinosus) also ranges into Central America.