New Primate Fossils Support "Out of Africa" Theory
for National Geographic News
|October 17, 2005|
Researchers have discovered fossilized remains of two previously unknown primate species that lived 37 million years ago in what is now the Egyptian desert.
The ancient teeth and jawbones of the tiny, monkeylike creatures shed new light on the poorly understood evolution of early anthropoids, a suborder of primates that includes apes, monkeys, and humans.
The discovery, researchers say, is evidence that the common ancestor of living anthropoids arose in Africa and that anthropoids have been evolving on the now separated Africa-Arabia landmass for at least 45 million years.
"There is now a consensus among specialists that the living anthropoidswhat paleontologists call crown anthropoidsoriginated in Africa. And our discoveries and analyses strongly support that hypothesis," said Erik Seiffert, a paleontologist at Oxford University in England.
Seiffert is the lead author of the study, which was reported last week in the journal Science.
The well-preserved pieces of teeth, jaw, and facial bones belong to two new species, named Biretia fayumensis and Biretia megalopsis. The fossils were discovered at a site in the Fayum desert region in northern Egypt.
The monkeylike species were tiny, with estimated weights of three-fifths and four-fifths of a pound (270 and 380 grams) respectively.
The researchers found that the upper molar tooth roots from Biretia megalopsis were exposed and truncated within the eyesocket. This suggests the roots had to make room for the larger eyeball of a nocturnal animal.
"With the sole exception of the South American owl monkey, all other living and extinct anthropoids have relatively small eyeballs" and are, or were, active during the day, Seiffert said.
Previously scientists found a single tooth attributed to another Biretia species. But that one tooth was the only anthropoid fossil known from a 10-million-year gap in the African primate fossil record between 35 and 45 million years ago.
"Very little could be said about Biretia on the basis of that single tooth," Seiffert said. "But now we have much more complete materialupper and lower jawsthat gives us a better idea of what Biretia is and how it fits into the broader picture of early anthropoid evolution."
Out of Asia
The findings show that anthropoids had branched into many species by the time of Biretia.
The two new species are members of a group called parapithecoids, or possible "stem" anthropoidsearly creatures from which the subsequent crown anthropoid line, including humans, arose.
The new species help fill in the gap between later anthropoids and the oldest undisputed anthropoid: Called Algeripithecus, it lived around 45 million years ago and was found in present-day Algeria.
Seiffert's analysis also suggests that a 57-million-year-old primate known as Altiatlasiuspreviously discovered in Moroccois an anthropoid.
While crown anthropoids may have originated in Africa, the most likely place of origin for even older stem anthropoids is in Asia. (Stem anthropoids are the first species to branch off on the anthropoid side of the family tree after their split with tarsiers, a genus of nocturnal primates.)
"Possible fossil anthropoids, such as eosimiids, as well as living and extinct tarsiers and a number of other, more distant primate relatives appear to have originated [in Asia]," Seiffert said.
But fundamental questions remain to be answered about anthropoid origins in Asia and Africa. The early and middle Eocene epoch (55 to 40 million years ago) was a period of active intercontinental exchange of land mammals between Asia and Africa.
"From the most recent data, it is now accepted that anthropoids originated in Asia," said Jean-Jacques Jaeger, a paleontologist at France's University of Montpellier, who wrote an accompanying commentary in Science.
"But when did they immigrate into Africa?" Jaeger said. "This is still a point of hectic debate."
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