Monkeys

There are at least 145 living species of the suborder Anthropoidea . Over 90% of them are monkeys. The remaining species are apes and humans. The anthropoids (members of the suborder Anthropoidea) have been the most successful primates in populating the earth. They are generally larger, more intelligent, and have more highly developed eyes than the prosimians.

There are two distinct infraorders of Anthropoidea that have been evolving independent of each other for at least 30,000,000 years. They are the Platyrrhini (New World monkeys) and the Catarrhini (Old World monkeys, apes, and humans). These two diverse groups of species can be distinguished from each other most easily based on the form of their noses and by the number of specific types of teeth.

The platyrrhine nose (on the left below) is relatively flat with somewhat sideways projecting nostrils separated by a wide septum. In contrast, the catarrhine nose (on the right below) has more downward projecting nostrils separated by a small septum.

Nose comparison of an emperor tamarin (left)

and a Celebes black macaque (right)

All primates have essentially the same kinds of specialized mammalian teeth adapted to eating a wide variety of foods. Beginning at the front, each quadrant of the mouth has 2 incisors, 1 canine, and varying numbers of premolars and molars. The incisors are used like scissors for nipping off pieces of food. The pointed canines are for piercing and tearing. The premolars and molars, with their cusps, are used to grind and smash food. In platyrrhine species, there are 3 premolars and 2 or 3 molars. This results in a dental formula of 2.1.3.2 or 2.1.3.3. In contrast, all of the catarrhines have 2 premolars and 3 molars, making a dental formula of 2.1.2.3. The chimpanzee shown below is an Old World anthropoid species and, therefore, has a catarrhine dental formula.

Catarrhine 2.1.2.3 dental formula

(common chimpanzee)

All Old World monkeys, apes, and humans share this 2.1.2.3 dental formula. This not only sets us apart from New World monkeys and prosimians, but it also reflects the evolutionary closeness of the Old World anthropoid species. By comparison, the general placental mammal dental formula is 3.1.4.3.

Patas monkeys in an African

grassland environment

In addition to these differences, New World monkeys are almost exclusively arboreal and most of them are smaller than Old World monkey species. Some Old World monkeys and apes are semi-terrestrial. If you see a group of monkeys casually walking around in a grassland environment (like those shown on the right), you can be sure that they are from the Old World.

Many of the larger