The cast of a skull believed to be from the oldest human ancestor (right) was cracked and distorted by the weight of the earth under which it was buried for millions of years. The computer reconstruction (left) reveals strong evidence that the owner walked upright and had a face more humanlike than apelike. (Staff photos Kris Snibbe/Harvard News Office)

Who or what was Toumai? Those who found his skull in 2001 insist he is the oldest human ancestor, a small fellow who lived by an African lake some 7 million years ago. Doubters have maintained that the skull belongs to an ancient chimpanzee or a gorilla.

More recent findings, announced last week (April 7), include teeth and jaw fragments unearthed in Toumai's neighborhood. Together with a reconstruction of his cracked skull, they support the idea that he was more man than ape.

When the skull was first found, Daniel Lieberman, a professor of anthropology at Harvard, called it "one of the greatest discoveries of the past 100 years." After studying the new evidence, Lieberman stands by that statement. "The next oldest, reasonably complete humanlike skull we have is just over 3 million years old," he notes. "The Toumai fossils go back close to the time when anthropologists believe our ancestors separated from chimpanzees."

In 2001, Michel Brunet, from the University of Poitiers in France, led a team who found the cracked and distorted cranium, along with two lower jaw fragments and some teeth, in a blisteringly hot, arid part of Chad, in north central Africa. The discovery pulled up the tree of evolution by its roots.

Brunet and his team named the creature Toumai, which means "hope of life" in the local language. It's a name often given to newborns in Chad. The fossils make him out to be about 3 to 4 feet tall, with thick brow ridges, and a flat, somewhat humanlike face. Close examination of the new teeth and jaw parts lead to the conclusion that they are of the same ancient age and belonged to creatures like Toumai.

The fossils are pictured and described in two articles in the April 7 issue of the journal Nature. The two reports are the product of an international collaboration among Brunet and his colleagues at the University of Poitiers; Lieberman; David Pilbeam, a professor of anthropology at Harvard; and researchers from the University of Zurich in Switzerland and from Chad.

Anthropologist Daniel Lieberman holds replicas of a 7 million-year-old skull that had a face and teeth more like a human than like the ape and gorilla skulls hanging in his laboratory.

Walking clues

Neither Lieberman nor Pilbeam did any digging in Chad, but they and former Harvard postdoctoral fellow Franck Guy closely studied the old and new evidence. They were particularly intrigued with what they saw when they cooperated with Brunet's team and researchers at the University of Zurich to restore Toumai's beat-up skull with the help of sophisticated computer techniques. Details of the skull and its relation to his face reveal that Toumai's neck would have pointed downward when he walked or stood up. That's typical of humans, not of apes and other knuckle walkers.

Another clue comes from a bony area at the base of the cranium, called the nuchal plane. It projects backward from near the spine and provides attachment for muscles that help balance the head when someone walks or runs. In Toumai, it angles gently upward, indicating that he could hold his head straight while walking on two legs. In apes, that angle is much steeper, indicating that they walk on all fours.

"This skull possesses many features suggesting that Toumai habitually walked upright," Lieberman says. "We don't know this with absolute certainty; we'd need to have a pelvis or limb bone to be sure." However, the evidence is strong enough to convince the research team that Toumai was a biped.

"Toumai suggests bipedalism was the key difference between very early human ancestors and apes," Lieberman continues. "Upright walking might literally have been the first step towards becoming human."

What's more, Toumai boasts a more humanlike face than hominids who lived even millions of years later. (Hominids include all non-apes up to modern men and women.) Take Lucy, the upright hominid who lived in eastern Africa some 3.2 million years ago. Her face is more apelike. Her snout is long and curved. Toumai's snout is shorter and flatter.

Lieberman admits, "We don't know what's going on here." It may be that Lucy comes from an extinct line of hominids. Perhaps, like other hominids, she went off on a dirt road that ended in the woods of extinction rather than traveling the paved highway from apes to modern humans.

One thing Toumai has in common with much younger and larger male hominids is a large heavy brow. "Such a brow ridge screams ‘male,'" says Pilbeam. "This is important because small male canine teeth are also an important defining feature of hominids, and Toumai's canines are small."

Getting teeth into it

More clues to Toumai's identity were found in the teeth scattered near his skull. These molars and canines and some jaw fragments come from six to nine different individuals, but they are more human than apish. The canines, especially from males, are small. And the molars — chewing teeth farther back in the mouth, are larger and thicker than those of apes. Chimps' molars are generally smaller and possess thinner enamel coatings.

No one knows what these humanlike creatures sank those teeth into, but apparently there was plenty of food available. Today, the place where their remains were discovered is a hot, bleak, remote desert constantly swept by blowing sand. Seven million years ago, as animal and plant fossils show, it was the site of a lake with grasslands and trees nearby. Ancient fish swam in the lake, along with crocodiles. On land, elephants and antelope roamed, rodents scampered, and monkeys swung in the trees.

Such fossils are key to dating Toumai's remains. Animals much like these lived farther east in what is now Kenya, and roamed over volcanic soils that contain minerals easy to date. That doesn't give a precise number, but a possible range of 6 to 7 million years. As researchers have refined this number, it has moved a bit closer to 7 million.

So there you have it. Longer ago than anthropologists ever imagined before, one of our ancestors was walking around near the southern edge of the Sahara desert. Although you wouldn't hail this short, big-browed fellow as a cousin, Toumai certainly seems to have been more like us than any other animal of that time.

These fossils give researchers and others concerned about our deep past plenty to think, or argue, about. The evolutionary path from ape to man was once compared to a straight ladder. As fossils accumulated, a luxuriantly branching tree became needed to account for all the different hominid skulls, leg bones, arm bones, jaws, and teeth that were discovered. But, notes Pilbeam, "at the base of this tree, there might well have only been one hominid for the first few million years. And that one may have been like Toumai."