Pygmy marmosets, which have long held the title of the smallest monkeys in the world, make their homes in the rainforests of the Upper Amazon Basin. Be sure to keep a keen watch for these tiny primates on your small-group cruises (see this post about Amazon wildlife sightings ). These little creatures stick to lowland forests and spend their days swinging through the trees along the banks of the Amazon River .
“Our naturalists  must have had binoculars for eyes,” said Amazon River cruise guests Betty and Steve Wing. “To see pygmy marmosets three times was unbelievable!”
These marmosets are not the smallest primates in the world, as the pygmy mouse lemur holds that claim. However they are the smallest of the monkey family, standing about five inches tall with eight-inch-long tails. These creatures live in small family groups consisting of an adult couple and their young, up to 15 members. Each group lives in an area of about one acre, which the monkeys will defend from predators and other marmosets by crying out and displaying their genitals. Marmosets will prowl about one third of their land each day looking for insects, fruit and plant buds to feed on. They also chew holes in certain trees and drink the sap, gum, resin and latex found within.
Pygmy marmosets typically give birth to fraternal twins, and older offspring will help care for the young until they reach maturity, which takes anywhere from one year to 18 months. While these creatures are small, they have a relatively long life expectancy of more than 11 years. When babies are born, they have pale yellow coats of fur except around their heads, which are dark gray with yellow highlights. Adult pygmy marmosets are covered with golden brown fur peppered with black and gray. Their tails are ringed in black, a common occurrence among marmosets.
When pygmy marmosets are swinging through the trees, they are able to dangle from a branch by just their fingernails. The nails are more like claws, long and tough, than flat fingernails that grow on other primate species. These nails and their tiny bodies, which weigh less than one-third of a pound, make it easy for the pygmy marmosets to move through the tree branches with ease. Their quickness, combined with their naturally camouflaged fur, makes it tricky to spot these tiny primates.