Toumaï's skull sparked controversy when it was unveiled in 2002.© Nature

The virtual reconstruction of a skull unearthed at the base of the Saharan dunes in northern Chad may dispel controversy over whether its owner was human or ape, says a team of palaeoanthropologists.

The skull, nicknamed Toumaï, along with teeth and a lower jaw was excavated by a team led by Michel Brunet of the University of Poitiers, France. The find was unveiled in 2002 and dated to about 7 million years ago (see ""Oldest member of human family found":http://www.nature.com/news/2002/020708/full/020708-12.html"). Based on the size and shape of the teeth and skull base, Brunet's team assigned Toumaï to a new species, Sahelanthropus tchadensis, the 'man of Chad'.

Some anthropologists disagreed with the researchers' claim that S. tchadensis is the oldest known member of the hominid lineage, making it more closely related to us than to other apes. They argued that the features Brunet and colleagues were calling human-like, especially parts of the skull, were actually more gorilla-like.

However, new teeth and jaw specimens from the Toros-Menalla site in Chad and a digital representation of Toumaï's head, reported in this week's Nature¹,², build on the original findings, says Brunet. "Now it's completely confirmed that Toumaï is not a chimp, or a gorilla, but a true hominid," he says.

Tooth seekers

The new teeth samples verify that Toumaï had small canines, alongside large molars and premolars that had thick enamel. Such a pattern is similar to that of later members of the human family.

The virtual reconstruction, led by Brunet's colleague Christoph Zollikofer at the University of Zürich-Irchel in Switzerland, uses a high-resolution computed tomography, or CT, scan to show what the fossil would look like without its cracks and other distortions.

"It's a big step forward," says anthropologist Clark Howell of the University of California, Berkeley. "These people are masterful at what they do."

The reconstruction shows that the opening in the base of the skull through which the spinal cord passes, called the foramen magnum, is oriented so that the neck points downwards. But in apes, such as gorillas, the neck point backwards, explains Dan Lieberman, a palaeoanthropologist at Harvard University in Cambridge, Massachusetts and a member of Brunet's team.

The virtual reconstruction shows that Toumaï probably walked upright with head held aloft.© Nature

This means that Toumaï's head balanced on top of its spine, suggesting an upright walking stance. "The evidence certainly suggests that Toumaï was a biped," says Lieberman.

However, Milford Wolpoff, an anthropologist at the University of Michigan in Ann Arbor believes that although Toumaï is related to the common ancestor of humans and chimps, it is not a hominid. Based on the reconstruction, he believes the site on the back of the skull where the neck muscles attach would support huge muscles, similar to those of apes. "This doesn't fit in the functional range of bipedalism," he says.

Lieberman, on the other hand, points out that all of the earliest known bipeds, such as the hominid Australopithecus afarensis, which is about half as old as Toumaï, had large neck muscles.

"This work confirms that Toumaï is the earliest and most complete hominid, and suggests that the earliest hominids were bipedal," claims Lieberman. "And that's big news." 

University of Poitiers, France

• References

  1. Brunet M., et al. Nature, 434. 752 - 755 (2005). | Article |
  2. Zollikofer C., et al. Nature, 434. 755 - 759 (2005). | Article |