N'DJAMENA, Chad, July 10 (UPI) -- An international team of researchers on Wednesday revealed the fossilized skull of a remote human ancestor that may be at least six million years old, making it roughly three million years older than the next-oldest find.
Judging by the size of the skull -- which researchers have nicknamed "Toumai" -- the creature probably was close to a chimpanzee in size and structure. Although the braincase is also chimp-like, the face and teeth more closely resemble those of humans, suggesting Toumai is a close relative of the last common ancestor of humans and chimps.
"It's a lot of emotion to have in my hand the beginning of the human lineage," research leader Michel Brunet of L'Universite de Poitier in Paris, said in a statement from Chad.
This new find is so revolutionary, it will have "the impact of a small nuclear bomb" on our understanding of human origins, said biological anthropologist Daniel Lieberman of Harvard University in Cambridge, Mass., who has seen the skull firsthand. "This is an astonishing find. It is easily one of the most important finds in the last hundred years," he told United Press International.
Although Toumai could be a direct ancestor of humanity, paleoanthropologist Bernard Wood of George Washington University in Washington, D.C., said he thinks it unlikely this new species -- scientific name Sahelanthropus tchadensis -- is the long sought-after "missing link" between humans and other primates. Instead, Toumai could be just one member of a huge, diverse and up-to-now undiscovered family tree of hominids -- all of humanity's relatives, distinct from chimps and apes, on which humanity is but one of many twigs.
"Quite simply, a hominid of this age should only just be beginning to show signs of being a hominid," Wood explained. "It certainly should not have the face of a hominid less than one-third of its geological age. Instead, at six to seven million years ago, "we are likely to find evidence of creatures with hitherto unknown combinations of hominid, chimp and even novel features."
Toumai, along with other skull fragments, was unearthed from the sandstone of the vast, flat, windy Djurab desert in northern Chad last July by undergraduate biologist Ahounta Djimdoumalbaye of the Universite de N'Djamena, who is described as the best fossil hunter among the team. Babies born close to the dry season in the Djurab are named Toumai, which in the local Goran language means "hope of life." Judging by the thick, prominent brow ridges, of a kind not seen outside the human lineage, Toumai probably was a male, the researchers said.
The discovery was made more than 1,500 miles west of Africa's Great Rift Valley, where the other fossils that comprise the entire picture of human origins so far have been found, Lieberman explained. However, Toumai is "older and completely different," he remarked. This means the tale of human origins therefore may be "far more complex and possibly very different from what we've been saying for the last 50 years."
Toumai lived in the midst of a critical interval in human evolution, about which almost nothing is known. All the fragmentary evidence could fit in a single shoebox. Until now, the first good records of hominids appeared five million years ago.
"This pushes back the origins of the human lineage by at least a million years," Lieberman said.
Along with the nearly complete skull, the international team of about 40 scientists from 10 countries, known as the Mission Paleoanthropologique Franco Tchadienne, found two lower jaw pieces and three teeth -- an incisor, a canine and a molar. All appear to belong to other members of this newfound species.
There are no nearby volcanic deposits around the find, and the hominid lived long before human ancestors used campfires, so direct age measurements using radioactive decay methods such as carbon dating are possible with Toumai. However, his remains were found near the bones of other animals -- crocodiles, three-toed horses, fish, hippos, turtles, rodents, giraffes, snakes, antelopes and a large wild boar -- whose ages have been ascertained from digs in Kenya using isotope dating. Their evolutionary level reliably places Toumai's age at close to seven million years, "so the divergence between chimp and human must be even older than we thought before," Brunet said.
So far no limbs, ribs or other bones have been discovered, which makes it difficult to judge whether Toumai was a knuckle-dragger or walked regularly on two feet. Brunet hopes studying the tooth enamel will help determine the creature's lifestyle and eating habits.
The research is reported in the July 11 issue of the British journal Nature.
(Reported by Charles Choi, UPI Science News, in New York)
