Squashed skull: The flattened cranium of Toumai, a key hominid fossil whose age is being hotly contested.
PARIS: A fresh storm has broken out over an ancient fossil presented by its defenders as a forebear of humanity and dismissed by its critics as the remains of a vulgar chimp.
Controversy has swirled around Toumai, the name given to the nearly complete skull, ever since it was found in the Chadian desert in 2001. Toumai's big defender is French palaeontologist Michel Brunet of The College of France in Paris, who says Toumai walked the Earth shortly after chimpanzees and hominids diverged from a common ancestral primate.
Critics are incensed that Brunet has given a hominid honorific - Sahelanthropus t chadensis - to a creature whose cranium, in their view, was too squashed to be that of a precursor to Homo sapiens. They calculate that Toumai's height was no more than 120 cm; or that of an adult chimpanzee.
Dating debate
Brunet appeared to have scored a knockout blow in February this year, when radiological measurements estimated that the soil where Toumai was found was between 6.8 million and 7.2 million years old. The study appeared in the U.S. journal, Proceedings of the National Academy of Sciences.
But the man who discovered Toumai, Alain Beauvilain of the University of Paris at Nanterre, has now publicly challenged this estimate. Beauvilain declined to take part in the hominid-versus-chimp debate, but questioned the dating methods used, and the way results were presented to the public. "It's time to set the record straight," he said.
In general, radiodating of sediment containing a fossil is considered to be a good guide to when the creature died, its remains eventually becoming covered by soil or other debris. But Beauvilain, a Chadian fossil expert, said that contrary to Brunet's claim that the fossil was "unearthed", the cranium was found loose on the sand.
A thick blue iron-based mineral found encrusting the skull showed clear signs of weathering from desert conditions, Beauvilain wrote in a recent commentary in the South African Journal of Science. He said the soil around the find - and possibly the find itself - had been shifted by wind or erosion, a phenomenon that can happen swiftly and frequently in the desert.
So carbon dating the soil and attributing that to the skull was a perilous exercise, he said. "How many times was it exposed and reburied by shifting sands before being picked up?" he wrote.
Beauvilain also takes issue with the soil samples used in the study, which were analysed by experts from France's National Centre for Scientific Research. He claims they were taken selectively and did not give a full picture of the depth and range of topography in which the find was made. He describes some of the collection choices as "astonishing".
On the same grounds, Beauvilain attacks Brunet's dating of an ancient Chadian jawbone, dubbed Abel and estimated to be between 3 and 3.5 million years old. Abel was also picked up on the surface in 1995, he said, and was not embedded in the soil.
Hominid origins
The debate is important because of its implications for anthropology. Toumai - the name means "hope of life" in the local Goran language - was found 2,500 km west of the Great Rift Valley, until now considered the cradle of humanity. So if the skull's dating is right, it implies the early hominids ranged far wider from East Africa, and far earlier, than previously thought.
The discovery also suggests that hominids evolved quickly from apes after they split from a common primate ancestry. Hominids are considered the forerunners of anatomically modern humans, who appeared on the scene about 200,000 years ago. Still unclear, though, is the exact line of genealogy from these small, ape-like creatures to the powerfully-brained Homo sapiens.
