#atelidae

Bolivian Red Howler Monkey (Alouatta sara), family Atelidae, Peru

Yellow-tailed Woolly Monkey Lagothrix flavicauda

A rare primate is found only in the Peruvian Andes. The species was thought extinct until 1974, when a group of scientists discovered a young yellow-tailed woolly monkey being kept as a pet in the city of Pedro Ruiz Gallo, Amazonas. The species is critically endangered.

Opposable thumbs have been a handy evolutionary tool for primates, but some monkeys can get by just fine without them! Spider monkeys only have four fingers, which makes it easier for them to swing from branch to branch.

(Image: A group of female Geoffrey's spider monkeys (Ateles geoffroyi) by Terry Whittaker)

A common woolly monkey (Lagothrix lagothricha) hangs from a tree in Ecuador

Colombian red howler (Alouatta seniculus), family Atelidae

The underside of the tail is bare of fur for the last third of its length, which helps with grabbing branches.