In the lowland Neotropical forests, Proechimys rodents are often the most abundant non-volant mammals.

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).

Thrichomys (punaré) Callistomys (painted tree-rat) Myocastor (nutria) Hoplomys (armored rat) Proechimys Reconstructing the systematics and phylogeny of Proechimys species have been greatly hampered by extreme levels of within- and among-population character variability.

[2] 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.

[13] Proechimys species presently occur mainly in South America, in all countries except Argentina, Uruguay, and Chile.