What is the world's smallest monkey?

According to PBS, the pygmy marmoset is the world's smallest monkey, at 5.35 inches in length and 4.2 ounces in weight on average. A tree-dwelling primate, the pygmy marmoset is notable for its sharp nails and impressive leaping ability.

The pygmy marmoset lives in the tropical rain forest canopies of South America where it feeds on the sap, gum and resin of trees. Insects and fruit also compose parts of its diet. Pygmy marmosets are social animals, living in small groups of two to nine individuals. The group is led by a dominant female who assumes all of the mating responsibilities.