New World Monkeys
The new world monkeys, or Platyrrhini, are a group of monkeys native to Central and South America.
New world monkeys diverged from old world monkeys between about 30 and 40 million years ago. At that time, the Atlantic Ocean was much smaller than it is today. The ancestors of modern new world monkeys may have arrived in the western hemisphere by drifting across the ocean on floating islands of vegetation.
There are a number of differences between new world and old world monkeys.
New world monkeys tend to be smaller than old world monkeys. The smallest monkey in the world, the pygmy marmoset, is a new world monkey. The average pygmy marmoset weighs about 4.2 ounces (119 grams) and is about 5 1/2 to inches (14 centimeters) long, excluding the tail.
The noses of new world monkeys face outward, and their nostrils are wide-set; old-world monkeys have downward-facing noses with close-set nostrils.
New world monkeys spend most of their time in trees. They often have prehensile tails - tails that can be used for grasping onto branches.
Some old world monkeys are arboreal while others are ground-dwellers. They do not have prehensile tails. However, they are more dexterous than new world monkeys. Old world monkeys have opposable thumbs; new world monkeys do not. Some new world monkeys have thumbs that are merely stubs or are missing altogether.
New world monkeys do not have ischial callosities - pads on the bottom of the buttocks. Old world monkeys have ischial callosities, which they use for sitting on the ground or on large tree branches. New world monkeys don't sit on tree branches; they lie across them.
The diet of new world monkeys consists mostly of fruit.
There are five living families of new world monkeys:
Atelidae - spider monkeys and howler monkeys
Aotidae - owl monkeys
Callitrichidae - marmosets and tamarins
Cebidae - squirrel monkeys and capuchin monkeys
Pitheciidae - uakaris, saki monkeys, and titi monkeys.
Many new world monkey species are endangered because of habitat loss, hunting and the pet trade.