Which rainforest mammal is famous for lacking functional thumbs on its front feet?

The colobus monkey is the rainforest mammal famous for lacking functional thumbs on its front feet.

Colobus monkeys have reduced or absent thumbs, while their other fingers remain long and well developed. This hand structure helps them move through branches and supports their specialized arboreal lifestyle.

The name colobus comes from a Greek word meaning mutilated, referring to the reduced thumb. Several colobus species live in African forests, including black-and-white colobus monkeys and red colobus monkeys.

Colobus monkeys are mainly leaf eaters, although they also consume fruit, flowers, buds, and seeds. Their complex stomachs contain chambers that help them digest fibrous plant material. They are also important prey for large forest predators, including chimpanzees and leopards.