A pygmy marmoset is the world's smallest monkey. A full-grown pygmy marmoset could fit in an adult human's hand, and it weighs about as much as a stick of butter. The newborn is about the size of a human thumb!
The father takes over their care. He carries the newborns piggyback style for their first two weeks, bringing them back to the mother to nurse.
Pygmy marmosets live in the Amazon region of Brazil, Colombia, Peru, Ecuador, and northern Bolivia.
They are very small but very quickly. Their fingernails are like claws to help them climb up and down tree trunks. They do not have opposable thumbs. The tail is not prehensile, but it helps the little monkey keep its balance as it gallops through the treetops.