The four creatures were small, weighing between four and 16 ounces, and resembled monkeys or lemurs.
The human family tree may have to be rewritten after scientists found evidence that the ancient ancestors of humans, apes and monkeys evolved in Asia - rather than Africa - tens of millions of years ago.
The astonishing claim follows the discovery of four species of early primate in the Sahara desert, dating back 39 million years.
The creatures - or anthropoid primates - are unlike anything seen before in Africa from the same time period or before, suggesting that they evolved elsewhere.
Scientists say there is overwhelming fossil evidence that mankind evolved from ape-like creatures in Africa, two to three million years ago.
The last common ancestor of humans and chimpanzees lived five to seven million years ago, while we split off from the gorilla branch of the family tree around 10 million years ago.
Many researchers have believe that the common ancestors of all apes, monkeys and humans also evolved in Africa.
But the new finding challenges that view.'If our ideas are correct, this early colonization of Africa by anthropoids was a truly pivotal event—one of the key points in our evolutionary history,' says Dr Christopher Beard, of Carnegie Museum of Natural History and an author on the paper in today’s Nature journal. When these anthropoids appeared, there was nothing on that island that could compete with them, he said.'It led to a period of flourishing evolutionary divergence amongst anthropoids, and one of those lineages resulted in humans.
If our early anthropoid ancestors had not succeeded in migrating from Asia to Africa, we simply wouldn’t exist.'Although the researchers found only fossilised teeth at the Dur At-Talah escarpment - part of the unspoilt, remote Sahara in central Libya - they have a rough idea of their size and shape.
“This extraordinary new fossil site in Libya shows us that 39 million years ago there was a surprising diversity of anthropoids living in Africa, whereas few if any anthropoids are known from Africa before this time,” he said.