Protopithecus was a genus of large Platyrrhine monkey that lived during the Pleistocene. Fossils have been found in the Toca da Boa Vista cave of Brazil, as well as other locales in the country.At an estimated weight of 22.6 kg (50 lb), it was the largest New World monkey known to exist. With slightly longer arms than legs, Protopithecus resembled the tree-swinging spider monkey, but its limb bones were nearly twice as thick.