These five genera share either four (Callistomys, Thrichomys) or five (Hoplomys, Myocastor, Proechimys) lophids on the lower deciduous fourth premolar, three roots anchoring the upper molars, and well-connected lophs on cheek teeth.

[1] Members display a variety of lifestyles including terrestrial (Hoplomys, Proechimys, Thrichomys), arboreal (Callistomys), and amphibious (Myocastor) adaptations.

On the other hand, Callistomys (painted tree-rats) is the sister group to Myocastor (coypus).

In turn, these two pairs of genera share evolutionary affinities with Thrichomys (punaré).

Thrichomys (punaré) Callistomys (painted tree-rat) Myocastor (nutria) Hoplomys (armored rat) Proechimys