Primates

Primates are mammals which have not become over-specialised but are adaptable opportunists. Primates include lemurs, monkeys, apes (and humans).

Surprisingly perhaps, a few monkeys including the Javan Brown Langur have shown a trend towards a reduction in thumb length; arguably an adaptation for under tree limb movement when thumbs would be in the way for reaching and grasping the next branch.

Gibbons and Siamang

Gibbons are distributed on the mainland and islands of Southeast Asia, spending most of their lives up in trees. Long arms and hooked hands are used for swinging (or 'brachiating') from branch to branch.