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The first primates

Life evolution table
• All dates are approximate

Archaic primates witnessed
the dinosaur extinction

The first archaic primates diverged more than 63 million years ago, so they probably shared the land with the last dinosaurs.
The extinction of non-avian dinosaurs was very advantageous to mammals.
Only the smallest mammals survived after a meteorite hit the earth, presumably 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 archaic primates were similar to present-day Prosimians.
Many think they looked like tree shrews.

Tree shrew
Tree shrew
© Anthony Cramp

About the size of a squirrel, they were insectivorous and possibly nocturnal.
They lived in the trees of tropical forests.

The first true primates
and the grasping big toe

The arrival of the first true primates coincides with a major climate event (PETM) that raised temperatures by more than 11˚F.
The oldest true primate fossil, called "Cantius", dates back to around 50 to 55 million years ago.
Cantius was about the size of a small domestic cat and had a grasping big toe with a flat nail at its extremity.
This opposable toe was equipped with powerful muscles and its position provided a better hold on small branches.
This improved the speed of these primates and added new routes when they needed to escape predators, it also permitted them to reach fruits that were unattainable by others.
Humans have lost this grasping toe feature when they stopped sleeping in trees.
However, the human fetus still develops a divergent big toe, then realigns it with the other four toes before birth.

Peaceful fruit-eaters

With better locomotion capabilities to flee from danger and a fruit-eating non-predatory lifestyle, the first primates lived rather peaceful lifes.
This led the females to have less babies and to take care of them for a longer period.
I propose that, since the claws weren't necessary anymore for locomotion or fight, flat nails evolved because our ancestors were now using them to groom themselves.
These early primates were clean animals.

Some characteristics of
the first primates

•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).

Using vision
rather than the other senses

The sense of sight of primates has evolved to become one of nature's best.
This indicates a strong reliance on vision when accomplishing everyday tasks.
•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.

Stereoscopic vision

Stereoscopic, binocular or 3D 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.

When you don't use a sense so much, it degenerates.
So our smelling, hearing and touching abilities have gradually diminished over time.

Additional primate traits

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 slender 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 facial expressions and their intelligence.


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