There are a few important differences between Old World monkeys and apes. Old World monkeys, like baboons and macaques, have tails and a great deal of agility, enabling them to jump and swing from tree branches.
Apes, which include gorillas and chimpanzees, are tail-less and tend to have a more upright posture. Scientists agree that Old World monkeys and apes share a common ancestry, but at some point two lineages diverged, one giving rise to the Old World monkeys and another to both apes and humans. Exactly when the split happened is a matter of debate.
A primate skull unearthed outside of Mecca in Saudi Arabia is the closest common ancestor to apes and Old World monkeys, researchers say, and helps date the split. Sediment records indicate that the fossil is 25 million to 29 million years old, making 24 million to 29 million years ago the window in which the monkey-ape split may have occurred. The ape and human lineages split later.
The research appears in the journal Nature.
“It is neither a monkey, nor an ape,” said Iyad Zalmout a palaeontologist at the University of Michigan and the study’s lead author. “You have an intermediate primate that tells you a story about Old World monkeys and apes.”
Based on the skull, the primate was medium-sized and weighed about 30 pounds to 40 pounds. It had broad upper molars and a long, baboon like snout.
A previous estimate, made with DNA samples of living primates found that the split occurred earlier, 34.5 million to 29.2 million years ago. There is however, no fossil evidence to support this.