What Are Primates?
Primates belong to a larger group of animals called mammals, animals that nurse their young with mother's milk. Present-day mammals vary widely, from elephants and rabbits to armadillos and kangaroos. Mammals first evolved around the same time that dinosaurs did, about 230 million years ago during a time known as the Triassic Period. Those mammals were small shrewlike creatures, but before dinosaurs died out around 65 million years ago, mammals began to diversify—to evolve into many different species. Some of the new mammalian species became the ancestors of present-day animals that may be close cousins of the primates, including bats, tree shrews (squirrellike mammals in Asia), and colugos (gliding cat-sized animals in Southeast Asia). And one of those early mammals became the ancestor of all primates.
The order (scientific grouping) of primates includes about 230 living species and more than 350 extinct species. All of the earliest primate species, which lived from about 65 million to 34 million years ago, are now extinct. Present-day primates range in size from 13 centimeters (5 inches) long to more than 2 meters (6 feet) long, and are divided into two major groups. One group, called the anthropoids, includes humans, apes, and monkeys. The other group, the prosimians, includes lemurs and lorises. Lemurs are long-tailed animals with long snouts and fluffy fur that live on islands off the east coast of Africa. Lorises are tree-dwelling animals found in Africa and southern Asia.
It is the versatility of primates, scientists believe, that has distinguished them from other mammals and enabled them to compete successfully for resources. Unlike most animals, which have features that make them ideally suited for specializing in procuring and eating one kind of food and occupying one particular habitat, primates are generalists. Many of their characteristics enable them to utilize a variety of resources and adapt to a variety of habitats. Humans, the most adaptable of the primates, live on every continent and in every climate zone. Nonhuman primates live mostly in tropical and subtropical regions, but they inhabit both forests and grasslands.
Another notable characteristic of primates is their brains, which are larger, relative to body size, than those of other mammals. This feature, in combination with other traits, has enhanced their adaptability. For example, the combination of large brains and large, forward-facing eyes enables primates to judge distances well. Paleontologists believe that this anatomy first evolved to aid in tree-climbing and sighting prey, but it also helps primates coordinate their eyes with the movements of their hands. And a larger brain means increased intelligence in general, useful for more than just getting from tree to tree.
Primates have other versatile features as well. A variety of teeth and a digestive system that handles a wide range of foods enable primates to eat a varied diet, including insects, fruits, small animals, eggs, leaves, nuts, and seeds—and in the case of humans, just about anything else on Earth. Primates have a bony bar that protects the outer sides of their eye sockets. They have flat nails instead of claws or hooves, and hands with five fingers—including a thumb—that enable them to grasp objects. These features make it possible for primates to carry food to their mouths. Because they do not have to root for food on the ground, primates typically have a short snout.
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