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Mammalian reptiles| The first primates |
Dinosaurs dominate the world First mammals Bird ancestors Marsupial mammals and Extinction of large dinosaurs First primates Whales enter the water Camel, pig and cattle ancestors Apes evolve Orangutans diverge Gorillas diverge humans diverge Homo Sapiens Bonobos diverge Earth's largest mass extinction First dinosaurs Expansion of grasslands| MILLION YEARS AGO |
EVENTS IN HISTORY |
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The extinction of non-avian dinosaurs was mostly advantageous to mammals.
Only the smallest mammals survived the heat wave after a meteorite hit the earth because they hid in deep burrows.
The absence of the dinosaurs left several ecological niches accessible for mammals who diversified into many new forms.
The first primates diverged less than one million years after the extinction of the dinosaurs.
Primates are relatively modern, when you consider life started on earth some 3.5 billion years ago.
The first primates, who lived about 65 million years ago, were similar to present-day Prosimians.
Many think they looked like tree shrews.
| Tree shrew |
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| © Anthony Cramp |
About the size of a squirrel, they were insectivorous and possibly nocturnal.
They lived in the trees of tropical forests.
•Replacement of the claws by flat nails. This was thought to be an adaptation to arboreal life, but it didn't make much sense. Now we know that flat nails have evolved as a grooming tool. These early primates were clean animals.
•Development of sensitive tactile pads on their digits.
•Increased independence and mobility of the fingers with an opposable thumb to aid grasping.
•Uprightness of the trunk, an adaptation to vertical positioning in the trees, hints towards future bipedalism (walking on two feet).
•Shortening of the snout and reduction of olfactory capacities.
•Major enhancements in vision (see below).
The sense of sight of primates has evolved to become one of nature's best.
Scientists are still searching the reasons why this happened, but it surely indicates a strong reliance on vision.
When you don't use a sense so much, it degenerates, so that smelling, hearing and touching abilities were gradually reduced.
Here's what happened;
•First, the eyes became bigger with their orbits completely encircled by a bone to protect them.
•Second, they moved from the side of the head to the front of the face.
This setup permits stereoscopic vision, with enhanced perspective in the overlapping center part that we call three dimensional vision.
A horse, for example, can almost see its tail, but has a very limited binocular field in the front.
•Third, primates have developed trichromatic color vision.
It uses three channels for color perception.
Most other mammals have dichromatic vision, with only two channels.
They see the world in 10,000 colors, while we see it with one million.
No particular characteristic or feature is unique to primates and can describe them all.
Primates are sociable animals found in tropical and subtropical regions.
Since they live in trees, their bodies have adapted to this type of living.
The propagation of fruit producing trees is closely linked to the success of primates.
Primates have a longer gestation period and a single child is born with its eyes open.
Primate mothers are among the best and they take care of their young for longer.
Primates are also known for their intelligence.
