Of the remaining families of the Simplicidentata, all are southern, the cavies (Caviidae), chinchillas (Chinchillidae), and degus (Octodontidae) being Central and South American, while the Capromyidae are common to southern America and Africa, and the Ctenodactylidae are exclusively African.
As in the agoutis (Dasyproctidae), the milk-teeth are long retained,, while in the allied cavies (Caviidae) they are shed before birth.
In the family Caviidae, typified by the cavies (or guinea-pigs), may be included a large number of South and Central American rodents, among which the agoutis and pacas are often ranked as a family (Dasyproctidae) by themselves.
The Caviidae, in the present more comprehensive sense, include the giants of the rodent order.
Capybaras belong to the family Caviidae, the leading characteristics of which are given in Rodentia.