Ancient fossilised teeth of small anthropoid monkeys discovered in Libya suggest our earliest ancestors may have migrated from Asia to Africa, according to newly published research.
The origin of anthropoids - primates including monkeys, apes and humans - has long been a source of hot debate among palaeontologists.
Experts have long argued anthropoids first appeared in Africa - but recent studies suggest an earlier Asian origin, dating 55 million years ago.
Now new fossils, dating 38 to 39 million years ago and discovered in Dur At-Talah in central Libya, further complicate the debate.
They reveal the existence of three types of African anthropoids - the oldest discovered on the continent to date, according to the study published in the journal Nature.
Based on previous discoveries in Egypt and Algeria, "we are aware until now of only one form of anthropoid primate, dating back 37 million years ago for the oldest," says one of the study's authors, Professor Jean-Jacques Jaeger, of Poitiers University in France.
"Here we have gone further, to 39 or 38 million years, and we have three (types) ... and among the three, there is an Asiatic form," he says.
"This therefore signals the direction of migration from Asia toward Africa."
Looked like marmosets
The teeth appear to have belonged to tiny primates, weighing between 120 and 470 grams in adult form.
"They looked more like marmosets than rats," says Jaeger. "They had the same prehensile hands with an opposite thumb, nails rather than claws, certainly a tail that served for balance when they climbed or jumped from one branch to another."
Their diminutive size also suggests our history began small, he adds.
The recent discovery also poses another question: Did all three types of anthropoids originate in Asia or were they the product of an initial diversification that took place in Africa?
Jaeger's group favours the Asia hypothesis.
"We have the impression it was a relatively significant population movement that most likely took place during the same time," he says.