Humans and apes are the only living members of a once diverse superfamily of primates, called Hominoidea, that thrived in East African forests beginning about 23 million years ago. Early hominoids are generally characterized as robust, slow moving, tree-dwelling primates that lacked the specializations of their descendants--for instance, the adaptations for suspension in trees or for knuckle-walking on the ground seen in modern apes. But like the apes, these early forms had pronounced snouts, relatively large and complex brains, flexible joints and they also lacked tails.
A Missing Link?
A skull found in Africa is from a relatively small-bodied species of the hominoid genus Proconsul. Among known early hominoids, Proconsul likely bore the closest resemblance to the last common ancestor of all modern apes and humans.
Many of the most complete Proconsul fossils have been found on Rusinga Island in Lake Victoria, Kenya, where scientists continue to search for fossil primates. At the time of Proconsul, the area was covered by lush forests.
About 14 million years ago, some early hominoids, well adapted for life in dense forests, began to be replaced by "advanced" forms better able to move through the open woodlands that were becoming increasingly common in East Africa. Also at about this time, the landmasses of Africa and Eurasia came into contact, allowing the interchange of animals between the two. Hominoids moved into Asia and monkeys once confined to Eurasia now diversified and thrived in East African woodlands. Perhaps as a result, the variety of hominoids began to dwindle. Today only a few groups survive--gibbons, orangutans, gorillas, chimpanzees and humans.
Sivapithecus--a hominoid that thrived from about 12 to 7 million years ago--closely resembles orangutans in skull structure. As such, Sivapithecus is a plausible direct ancestor of orangutans. But Sivapithecus' unspecialized body, much like those of earlier hominoids but unlike those of modern orangutans, suggests a more complex evolutionary relationship.