The rock cavy or mocó (Kerodon rupestris) is a cavy species endemic to eastern Brazil which has also been introduced to the Atlantic island of Fernando de Noronha. The rock cavy is called mocó in Brazilian Portuguese, and koriko pexerumen in the Xukuru language of Pernambuco, Brazil. Description The rock cavy is a fairly large rodent weighing up to . Like other cavy species, their tails are vestigial or absent. Their backs are grey-brown and their bellies tan to light brown. In appearance and habit, they closely resemble the unrelated African rock hyraxes (an example of convergent evolution). They are herbivorous, feeding on seeds and leaves of the scrubby vegetation that grows in their territories. This vegetation consists of tender leaves and certain species of creeper. Distribution and habitat Rock cavies are found in dry, rocky areas with low, scrubby vegetation, and they prefer to reside close to stony mountainsides and hills. They are native to eastern Brazil, from eastern Piauí state to Minas Gerais state, and have been introduced to the island of Fernando de Noronha, off the eastern coast of Brazil. Phylogeny Rock cavies belong to the order Rodentia, suborder Hystricomorpha, based on their porcupine-like jaw muscles. They are in the family Caviidae (guinea pig-like rodents), which has three subfamilies (formerly two); rock cavies have recently been placed in a new subfamily Hydrochaerinae, with the capybaras, and with the closely related rainforest-dwelling acrobatic cavy. Behavior Rock cavies usually shelter in crevices. They may be seen resting at all times of day, but are crepuscular – active mostly at dawn and dusk. They are able to climb, which makes reaching leaves, seeds, and occasional fruits easier. Rock cavies live in groups, centered around rock-sheltered dens. Each rock cavy group has an alpha or dominant male and several females. The males are territorial, defending rock pile shelters against other adult males. The rock piles are chosen to impress the females; once a female chooses a rock pile, she indirectly chooses its guardian as her mate. They can sometimes display homosexual behavior, with males courting other males. Some paedophilic behavior has also been displayed, with adult males courting juvenile males. Studies show that rock cavies have a direct link between their retina and the mediodorsal nucleus in the thalamus, which may provide them with strong visual recognition, emotional learning, and/or enhanced object-reward associative memory. This may partly explain why they are