actually they both aren't the smallest primates. the madame berthe's mouse lemur is actually believed to be the smallest primate in the world. they only weigh about 30g. the pygmy marmoset however is the smallest monkey weighing about 100g. the pygmy tarsier weighs about 60g but they may or may not be extinct.

I know it is either the marmoset from the Amazon rainforest or the tarsier from Indonesia, and both can be held in the palm of the hand of an adult human, but I'm not sure which is the smaller of the two.

Only need to know about living species not extinct ones.