South African Fossils May be Man's Oldest Ancestors

JOHANNESBURG, South Africa (April 25) - A collection of South African humanoid fossils is far older than previously thought, and may represent the oldest direct link to humanity, researchers said Friday.

After analyzing specimens with a new dating method, researchers from Johannesburg's University of the Witwatersrand said they had shown that remains from the world's richest hominid fossil site, the nearby Sterkfontein caves, were more than four million years old.

The new dates put the fossils on a par with specimens from the same Australopithecus group of species found in northern Kenya as humanity's oldest direct ancestors, and make them almost a million years older than scientists previously thought.

''The new dating for these old specimens from South Africa shows that we have contenders to be the earliest members of the genus Australopithecus yet found in Africa,'' said Professor Phillip Tobias, head of the university's paleontology team.

''We are right down here where our ancestors were almost certainly living,'' he said. ''This has reasserted South Africa's role in the direct ancestry of mankind.''

The announcement is sure to court controversy.

The age of hominid specimens dictates their standing in the evolutionary tree, and thus their credentials as ancestors of modern man's own genus Homo, members of which are thought to have walked in Africa some 1.5 million years ago.

The Sterkfontein fossils, including the oldest known complete Australopithecus skeleton, had previously been dated between two and three million years old by other research teams. But Professor Tim Partridge, the study's lead author, said the new dates were the best yet.

''There is going to be a lot of shouting going on, but I think that this will stick. I think these are very good dates.''

PAINSTAKING TECHNIQUE

The painstaking new technique, developed with the help of researchers at Purdue University, Indiana, in the United States, measures the amounts of nuclear isotopes of aluminum and beryllium in material surrounding the specimen.

The two decay at different rates from a known initial composition, allowing researchers to date a sample.

The work, published Friday in the American journal Science, puts the age of the Sterkfontein ''little foot'' skeleton at 4.17 million years old, and pegs that of new finds at the nearby Jacovec cavern at just over four million years.

Those dates compare with an age range of 3.9 to 4.2 million years for remains found near Kenya's Lake Turkana, thought to be the oldest Australopithecus specimen yet found.

Researchers see hominids of the Australopithecus genus as direct human ancestors, part of the now-extinct link between apes and modern man that has been the subject of inquiry and controversy ever since Charles Darwin proposed his theory of evolution in the 19th century.

The new dates imply that the Kenyan and South African Australopithicines were contemporaries, separated only by distance. It is possible that the two were actually of the same species, although the Sterkfontein team has not yet proposed a full taxonomic classification for its finds.

Previous dating techniques used as ammunition in arguments over the age of the remains had relied upon more circumstantial evidence from the magnetic structure of nearby rock layers and the presence of other fossils of known age.

Partridge said he anticipated criticism of the results to focus on the complicated structure of the Sterkfontein caves from where samples were taken. But the new technique did not rely upon knowledge of the rock strata, he said, adding that it was robust and would withstand scrutiny.

Reut11:19 04-25-03

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