They tended to be larger and they had larger brain on proportion to their body size.Perhaps the most important feature of the early primates is that they were arboreal; that is, while they exploited food sources on the ground as well as those in trees, for the most part they lived in the trees.
Because they lived in trees, early primates were subject to selective pressures that brought about a number of other changes. Moving through the trees required improved eyesight and motor coordination.
This led not only to the evolution of stereoscope sight with greater depth perception, which was needed for jumping from one branch to another, but also to color vision, which is useful in telling live branches from dead ones or ripe from unripe fruit.
Other senses changed along with eyesight. The sense of touch became more important, since the precision required for moving in the trees had life-or-dead meaning for primates. An animal that is running along on the ground can make a mistake in judgment, fall, get up, and be on its way again, but a slight mistake in the treetops can be fatal.
The forelimbs, or hands of primates therefore became more sensitive, and the fingers became more mobile. Claws were replaced by flat nails and most important the thumb and big toe became opposable, which means that they could be moved opposite to some or all of the fingers or toes.
This means that primates could manipulate objects with their hands, rather than grasping them with their teeth, as other mammals do. Later on, the arms, grew distinct from the legs and became able to rotate, flex, and extend.
All of these changes are important in terms of the way early primates gathered food and caught small animals both in trees and on the ground.
The Evolution of Primates
