About Primates

16th June 2010

Primates have a thumb and four fingers. This gives them the ability to grip with their hands and with their feet. They have a long flexible spine and a short flexible neck, which is linked to the chest by a collarbone or clavicle. This clavicle allows primates to hang from their arms without straining the shoulder muscles. Primates have larger brains than other animals, which means they can make maximum use of their environment and create more complex social structures.

They have “stereoscopic vision”, which means that because the eyes are forward-facing, the image seen through one eye overlaps the image seen through the other. This then gives a clear three dimensional image and so allows the primates to be a good judge of distance, essential for life in the trees.

Primates are split into two main groups: the “higher primates” and the “lower primates”. The “higher primates” consist of humans, apes, lesser apes, and monkeys. This group is considered to be more intelligent than the others because they have larger more complex brains. The “lower primates” or “prosimians” include lemurs, lorises, pottos, bushbabies and tarsiers. This group is considered to be less intelligent because of their smaller brains. As a result, most “lower primates” have different physical characteristics.

Higher Primates or Anthropoids Great Apes
Human Homo sapiens?Humans are different from other primates because they walk upright, lack a body full of fur and do not have an opposable big toe. In relation to the size of their body, humans have the biggest and most complex brain. Humans can be found throughout the world.

The higher primates also include chimpanzees (Pan troglodytes), bonobos or pygmy chimpanzees (Pan paniscus), gorillas (Gorilla spp. – 3 species) and orangutans (Pongo spp. – 2 species). These four great apes differ from other primates because they have larger bodies and are sexually dimorphic (males are larger than the females). They are considered to be more intelligent than all other primates except for the human. They are more terrestrial and build nests for sleeping and birthing and so lack the ischial callosities (bum pads). Great Apes and lesser apes both lack the tail. Apes are found only in Asia or Africa.

Lesser Apes Gibbons and Siamangs hylobatidae
Lesser apes also lack the tail and have a very upright body posture and a broader chest. Like great apes, lesser apes tend to hang from branches instead of balancing on top of them. The larger brains of apes result in longer gestation and maturation periods. Males and females of the same species are more or less the same size. Lesser apes are found only in Asia.

All primates that fall into the category of monkey will posses a tail, which is not to say that all tailed primates are monkeys. Monkeys are then further divided up into two separate groups depending on a number of different physical characteristics. These changes in physical characteristics have to do largely with their habitat. Monkeys can be found in South America, Africa and Asia.

New World “Platyrrhines” Old World “Catarrhines”
Are found only in South America. Are found in Asia and Africa.
Tree dwellers that do not often travel.
Live in a more varied habitat or feed on the ground.
The thumb sits in line with the other fingers and creates more of a scissor-like grip. More opposable thumb that rotates like ours.
Sit on their tails so lack the ischial callosities. (bum pads). Sit directly on the buttocks and so have ischial callosities which are pads on the bum.
Prehensile tails that can be used as a hand. Long straight tails used just for balance.
Males and females are the same size. Males are larger than females.
Platyrrhines = flat nose, nostrils far apart and open to the side. Catarrhines = down facing nose, nostrils open downwards.
Two extra molars compared to Old World primates. Same number of teeth as us with specialized premolars for sharpening the upper canine.
Lack cheek pouches. Have cheek pouches for storing food.

Lower Primates or Prosimians
Prosimians (“before apes”) are considered to be the most “primitive” of the primates. They are the least advanced, both mentally and physically. Prosimians have physical characteristics that resemble or are the same as other mammals.

For example: Prosimians have nocturnal vision (except tarsiers). The tapetum lucidum, a reflective layer in the retina enhances night vision. This reflective layer occurs in cats and is what gives the “glow in the dark” appearance to the eyes when a light is pointed at the face.

They have longer snouts than other primates, which means three things. The eyes are pushed further apart decreasing three-dimensional vision, the brain casing is smaller and they have longer nasal passages. The latter combined with a wet tip to the nose enhances their sense of smell. Prosimians therefore rely more heavily on scent then they do on sight.

Although they posses a thumb and four fingers, prosimians do not have the ability to use their fingers individually. Their hands are designed just for gripping and nothing else.

Grooming is therefore difficult by hand, so prosimians use their teeth. The front, bottom teeth form a “dental comb” that untangles hair and removes dirt. The dental comb is also used for biting bark off trees and scraping gum.?Hair and debris collects in the dental comb, which is cleaned out by the “sub-lingula”. The “sub-lingula” is a second tongue like a horny plate, which is situated under the tongue and slips through the teeth to clean.?Prosimians give birth to multiple offspring and so some species have more than two nipples.

As a result, the shape of the uterus and the type of placenta differs from that of higher primates.

It is important to remember that prosimians are a very diverse and interesting group of primates and are not categorized into any other group of mammals.