If it Looks Like A Primate...
By 57 million years ago, primates quite similar to modern lemurs had established themselves throughout the vast, humid forests that once covered much of Europe, Asia, North America and Africa. Compared with their earlier relatives, these early "modern" primates, called euprimates, had large brains, small snouts and forward-facing eyes--suggesting that, like modern primates, they relied more on vision and less on smell. Most important, euprimates boasted grasping hands and feet, a feature characteristic of most modern primates.
Unlike its primate ancestors, Notharctus tenebrosus had greatly elongated hind limb bones and very mobile forelimbs, features reminiscent of today's Sifaka lemurs from Madagascar. Sifakas cling to vertical tree trunks and use their powerful legs to propel themselves enormous distances through the air.
Get a Grip
Like other euprimates, Notharctus tenebrosus had grasping hands and feet with the first digit moved away from the others. Its thumbs, fingernails and touch-sensitive fingertips allowed Notharctus to grip and manipulate branches and other objects, laying the groundwork for tool use in later primate evolution.
The arid desert of western Egypt was a dense tropical forest 30 million years ago and was home to many kinds of primates. Among these primates were new forms that shared features with living "catarrhine" primates--Old World monkeys, apes and humans. These ancient primates had larger brains compared to their body size than their predecessors had, and possessed fully opposable thumbs and big toes, forward-facing eyes enclosed by bone at the rear and sides, and fairly small nasal cavities. As a result, they may have behaved much like their living descendants that rely heavily on their eyesight, are usually active during the day and have complex social organization.
All The Better To See You With
Aegyptopithecus zeuxis, a 30-million-year-old cat-sized primate, saw the world very differently than its ancestors did. It had forward facing eyes, which allowed for good depth perception. The small eye sockets, lined at the sides with bone, hint that Aegyptopithecus was active during the day and slept at night, as virtually all living catarrhine primates do.
Not All Hands (or Feet) are the Same
Primates are generally able to grasp objects with their hands and feet. But while "lower" primates such as lemurs usually clamp onto objects with their whole hand, "higher" primates such as monkeys can manipulate small objects with their fingertips.