The ancestors of monkeys, apes and humans were thought primarily to have originated in Africa, but now what may be the oldest examples of such fossils discovered yet on the continent suggest these primates might have originally arisen in Asia, researchers suggest.
The dating of the newfound fossils is controversial, however.
The origin of anthropoids — the simians, or "higher primates" — has been hotly debated for decades among scientists. Although a series of fossils unearthed in Egypt have long suggested that Africa was the cradle for anthropoids, other bones revealed in the last 15 years or so raised the possibility that Asia may be their birthplace.
Now paleontologists have revealed the earliest known African anthropoids found to date — three previously unknown kinds of the primates from Dur At-Talah in central Libya that apparently date back 38 million to 39 million years ago.
The anthropoids would have been remarkably small, with the adults weighing just 1/4 to 1 pound (120 to 470 grams). The fossils were also quite distinct from each other, showing that anthropoids were significantly more diverse at that early time in Africa than scientists had thought. This diversity is what suggests previous origins in Asia.
"This extraordinary new fossil site in Libya shows us that in the middle Eocene, 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," said researcher Christopher Beard, curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh.
The findings might suggest these primates spent far more time evolving and diversifying than before considered, but the researchers contend that anthropoids seem absent at earlier sites in Africa. As such, "this sudden appearance of such diversity suggests that these anthropoids probably colonized Africa from somewhere else," Beard said. "Without earlier fossil evidence in Africa, we're currently looking to Asia as the place where these animals first evolved."
"If this immigration of early anthropoids from Asia into Africa didn't occur, we wouldn't be here right now to discuss them," said researcher Jean-Jacques Jaeger, a paleontologist at the University of Poitiers in France. "Anthropoids apparently became extinct in Asia, but they apparently found excellent conditions in Africa to develop and evolve. If that never happened, there would be no mankind."
Vertebrate paleontologist Erik Seiffert at Stony Brook University in New York, who did not take part in this study, argues these new fossils are not as old as claimed, suggesting they only date back 35 million years. Jaeger defended the ages, noting that other fossils they discovered at the site and magnetic details in the rocks supported their interpretation. Paleontologist Richard Kay at Duke University in Durham, N.C., who also did not participate in this research, said "Seiffert's view is quite plausible, but so are those of the authors of this study."
Kay did note he had a problem with equating the absence of evidence of earlier anthropoids in Africa as evidence of their physical absence during that time. "I find that relatively implausible — the African fossil record at that time is terrible. More work in north Africa would be good, as well as work in south China and India, which could more definitely establish that is where anthropoids come from," Kay said.
Nevertheless, Seiffert does think evidence to date most strongly suggests that anthropoids migrated from Asia. Kay added that one of the Libyan anthropoids resembled one found in Asia, "reinforcing the similarities between the African and Asian groups."
The scientists detailed their findings in the Oct. 27 issue of the journal Nature.