1. A monkey is any primate that is not a human, prosimian (lemurs, sifakas, lorises, pottos, bush babies, and other primitive primates), or ape. Monkeys make up two of the three groups of simian primates, Old World monkeys and New World monkeys. The other group is the apes.
2. Brazil has more kinds of primates than any other country, with 16 genera and 77 species. The Democratic Republic of the Congo is second, with 18 genera and 37 species. As of 1999, 92 of the world's 192 nations have wild primate populations. As of 2008, there are 81 species of New World monkeys in the Amazon basin, and new ones are continually being discovered. There are 96 species of Old World monkeys.
3. Monkeys live in trees, grasslands, mountains, forests, and on high plains. A group of monkeys is called a troop.
4. Most primates share six basic features: forward-facing eyes, eye sockets, grasping hands, nails, fingerprints, and large brains. Monkeys are most easily distinguished from apes by their tails. Apes have no tails. Apes and spider monkeys swing arm-to-arm in trees, but most monkeys don’t. Instead, they run across branches. Monkeys can grasp with both their fingers and their toes.
5. Monkeys use vocalizations, facial expressions, and body movements to communicate. Grinning or pulling the lip is a sign of aggression in monkeys, along with yawning, head bobbing, and jerking the head and shoulders forward. Monkeys express affection and make peace with others by grooming each other.
6. The Pygmy Marmoset is the world's smallest monkey. It measures 4.5 – 6 inches (117-159 millimeters) in length and weighs 3 to 5 ounces (85 to 140 grams). The male Mandrill is the largest monkey. It is almost 3.3 feet (1 meter) long and weighs about 77 pounds (35 kilograms).
7. Howler monkeys are the loudest monkeys. Their howls can be heard for about two miles in the forest and almost three miles in an open area. Capuchins are skilled tool users. They smash nuts with rocks, insert branches into crevices to capture food, remove spines and hairs from caterpillars by rubbing them against a branch, protect their hands with leaves, and use large branches to club snakes.
8. Most monkeys eat both animals and plants. Some also eat dirt. Monkeys peel their bananas and do not eat the skins. The orangutan is the largest fruit-eating animal in the world and it rarely comes out of the trees.
9. Chimpanzees, gorillas, and orangutans all catch cold, but curiously monkeys do not. All monkeys like to be clean so they have a barber monkey clean out their fur. The barber monkey's payment is the bugs in its customer's hair.
10. Monkeys are seriously threatened by habitat loss--especially those that live in tropical forests, a habitat that is quickly disappearing. Twenty-one primate species are listed as critically endangered on the 2007 Red List of Threatened and Endangered Species. Forty-seven are endangered and 46 are vulnerable to extinction.