August 27, 2007
Monday

Fossil hunters tracing the long and tangled paths of evolution in Africa have discovered the remains of ancient apes, much like modern gorillas, that suggest a human lineage stretching back as far as 20 million years, when creatures like orangutans were among our earliest ancestors.

The team has found a collection of nine fossil teeth plucked from the hardscrabble dirt and rocks on the flanks of an old volcanic gorge in southern Ethiopia. Those teeth, they say, provide the best clues yet to determine the times when the common ancestors of great apes and humans first emerged in Africa.

Gen Suwa, an anthropology professor at the University of Tokyo, and Berhane Asfaw, director of the Rift Valley Research Service in Ethiopia, led an expedition two years ago to the remote fossil area 100 miles east of Addis Ababa, the Ethiopian capital, and returned again in March with Yonas Beyene, an Ethiopian archaeologist.

Their harvest on that first venture was only a single somewhat worn and very ancient canine tooth that appeared to have come from a female ape or a very young male, but when they returned this year, the team's sharp-eyed Ethiopian hunters found eight molars incised with patterns that clearly bespoke their gorilla origins -- well adapted to crush and chew tough, fibrous foliage -- the very diet of today's gorillas. The teeth may have come from at least three and probably six or more individuals, the scientists inferred.

Modern geneticists have sought to establish "molecular clocks" for the evolution of humanity's forebears, based on the rates at which genes are presumed to mutate. But to Suwa and Asfaw and their colleagues, those clocks could well be millions of years off -- and the fossils show dates much earlier than the molecular estimates, they say.

Their findings also indicate that the ape-to-human lineage must have had its earliest beginnings right there in southern Ethiopia, and not in Europe or Asia, as some earlier Eurasian fossil finds have suggested from discoveries in Spain, India and Pakistan.

The team's report on the newfound fossils was published Thursday in the journal Nature.

"The report is one of the most important" on the issues and "opens a window on the timing of evolution that we've never had before. This implies that the common ancestor of chimps and humans is much earlier than is currently claimed by geneticists," said C. Owen Lovejoy, an anthropologist and anatomist at Kent State University who was not connected with the research team.

The scientists have named their large ape Chororapithecus abyssinicus after Chorora, an Ethiopian village, and its surrounding geological formation where the teeth were found. "Pithecus" is Greek for "ape" and Abyssinia is the historic name for Ethiopia.

It took 60 miles of hiking across dry patches of ancient lava and sedimentary rocks with few shrubs before the first fossil was found -- what Asfaw called "something new -- Ethiopia's first fossil great ape."

It also took the most modern three-dimensional X-ray equipment, called microcomputed tomography, in Suwa's Tokyo laboratory to reveal the structure of the molars and establish that they were indeed from some kind of "proto-gorilla" and "shared with modern gorillas some unique specialization for eating fibrous foodstuff such as stems and leaves," as Suwa said in an e-mail description of the team's discovery.

The region is about 120 miles south of Ethiopia's Middle Awash region in the Afar desert that has yielded fossils of early humanlike creatures almost 6 million years old, and 160 miles south of Hadar, the famed site where the 3.2 million-year-old bones of Lucy were found.

Among the 330 fragments of fossil bones and teeth that the team found were the remains of many other ancestral animals, including early versions of elephants, rhinos, horses, hippos, swine, giraffes and cloven-hoofed beasts such as cows, bison and antelopes.

The scientists estimate that the gorilla lineage must have evolved from a common ancestor of orangutans about 20 million years ago, that gorillas and chimpanzees then split from some earlier common ancestors about 12 million years ago and that the last common ancestor of chimps and hominids -- the first creatures in the human lineage -- must have lived about 9 million years ago.

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