Skull May Shift
Wed Jul 10, 3:40 PM ET
By MARK EVANS, Associated Press Writer
In what may be the most startling fossil find in decades, scientists in central Africa say they have unearthed the oldest trace of a pre-human ancestor — a remarkably intact skull of an apelike species that walked upright as far back as 7 million years ago.
The thick-browed, flat-faced skull was found in Chad, 1,500 miles west of pre-human discoveries in east Africa.
Exactly where the skull fits into man's family tree is not clear. But the skull's age, shape and location challenge basic beliefs about the evolution of man's earliest ancestors.
Among other things, the find could push back the date at which humans are believed to have diverged from apes. And it suggests that upright-walking human ancestors evolved not just on the grasslands, as anthropologists have long thought, but in forests as well.
Scientists nicknamed the specimen Toumai, or "hope of life" in Africa's Goran language.
It was uncovered a year ago by a 40-person research team led by French paleontologist Michel Brunet in a remote, wind-scoured stretch of desert that was a lush forest long ago. Details appear in Thursday's issue of the journal Nature.
It is the culmination of a lonely and sometimes dangerous search by Brunet that began 25 years ago, far from the most celebrated excavations in east Africa. Besides having to deal with the harsh climate, the researchers had to dig carefully around land mines left from decades of war.
"It's a lot of emotion to have in my hand the beginning of the human lineage," Brunet said in a statement. "I have been looking for this for so long."
Other scientists who have examined the skull said it is a landmark, but enigmatic, specimen.
"It's not what we thought we would find," said Bernard Wood of George Washington University. "If you at the back of it, it looks like a chimpanzee, and if you look at the front of it, it looks like something in the human fossil record unambiguously a couple of million years ago."
Harvard anthropologist Dan Lieberman said the skull raises "a wheelbarrow full of questions." He likened it to Raymond Dart's 1920s discovery of a skull of an "ape-man" in southern Africa, which lent the first support to Charles Darwin's theory that the deepest traces of human evolution could be found on that continent.
"It's a major find," Lieberman said. "It will take many years for us to understand just how important it is."
Other researchers were more guarded.
"This is a great extension onto the fossil record," said University of California paleontologist Tim White. "But that's what the real story is here — it's an opening window."
Indeed, Toumai is the oldest addition to a growing array of recently discovered hominid, or pre-human, fossils that show human evolution was not an orderly progression.
Instead, Africa appears to have been widely populated with many different transitional species. How they get sorted into a new edition of the human family album could take years to settle.
Toumai was classified as a member of the newly dubbed species Sahelanthropus tchadensis and is thought to be between 6 million and 7 million years old.
That means it could be as much as 1 million years older than previously found hominid fossils, and at least 3 million years older than the next-oldest hominid skulls.
Brunet concluded Toumai walked upright because the hole for the spinal cord at the skull's base is shaped like those of more recent bipedal prehumans.
The skull appears to be the size of that of a modern common chimpanzee with a similar cranial capacity and smallish teeth. But facial details, such as a very thick bony eyebrow ridge, are like those of male hominids.
The specimen's age falls near a critical point when the human lineage split from apes. Relying on genetic evidence, scientists have assumed the split occurred 5 million to 7 million years ago; Toumai's appearance may push back the timeline.
Also, Toumai challenges the notion that human ancestors evolved only on the east side of the African Rift Valley running from the Red Sea to Mozambique.
The east side of the rift during prehistoric times consisted of savannah. Scientists believe that with few trees to climb, pre-humans had to walk upright to see over the tall grass.
West of the Rift Valley, the ancient landscape was lushly forested. Scientists have long believed that apes remained in trees there and failed to evolve into upright-walking creatures. But the Toumai discovery suggests otherwise.