The black-striped capuchin (Sapajus libidinosus), also known as the bearded capuchin, is a capuchin monkey from South America. It was the first non-ape primate in which tool usage was documented in the wild, as individuals have been seen cracking nuts by placing them on a stone "anvil" while hitting them with another large stone. Adaptations to carrying large stones and fruit include strengthened back and leg muscles that permit the monkey to walk on its hind legs while carrying stones. The black-striped capuchin has traditionally been considered a subspecies of the tufted capuchin. On the contrary, the southern population here included in S. libidinosus has sometimes been considered another species, Azaras's capuchin (S. cay) (syn. S. paraguayanus).