In general, the arboreal forms are most rat-like in appearance, whilst the burrowing species are more gopher-like, with stocky bodies and short tails.

[5][6] The following table recapitulates and compares the taxonomic content of taxa recognized on molecular and traditional basis: the two families Capromyidae and Myocastoridae, the five subfamilies Echimyinae, Euryzygomatomyinae, Capromyinae, Dactylomyinae, Eumysopinae, and the four tribes Echimyini, Myocastorini, Capromyini, and Plagiodontini.

The bristle-spined rat, Chaetomys subspinosus, has sometimes been classified in Echimyidae,[4] although traditionally considered a member of the New World porcupine family Erethizontidae.

The second major clade includes fossorial genera (e.g., Euryzygomatomys or Carterodon), a terrestrial one (Trinomys), and members inhabiting the Caribbean islands (Capromyidae).

Trinomys Clyomys Euryzygomatomys Carterodon Plagiodontia Geocapromys Capromys Mesocapromys Mysateles Thrichomys Hoplomys Proechimys Myocastor Callistomys Isothrix Lonchothrix Mesomys Pattonomys Toromys Makalata Echimys Phyllomys Diplomys Santamartamys Kannabateomys Dactylomys Olallamys