The Brazilian Cavy, also called the Brazilian Guinea Pig, is a wild rodent related to the domestic Guinea Pig and is native not only to Brazil but also to Argentina and much of northern South America.

Habitat is dry savannah and grassland. A medium-sized cavy, its fur is always grey-brown with a paler underside. Some dark or melanistic individuals are prevalent at least in captivity. Living in groups, they alert group members to a threat by a high-pitched scream.

The Rock Cavy is the only mammal endemic to the Caatinga eastern semi-desert region of Brazil. Guinea-pig-sized rodents, they are more closely related to the Capybara than to the "Cavia" species and have the square muzzle of the former. They are social and communicative creatures living in groups with a dominant male who builds or guards a rock shelter. They also shelter in rock crevices and climb well. Both parents care for the young. They are hunted for human food and have suffered habitat loss.