Youngster
Three million years! No, even four! Not true: there are only two! What sounds like an academic dispute among anthropologists has far-reaching consequences for human prehistory: If the re-dating of the Australopithecus fossil "Little Foot" is correct, it is ruled out as a direct ancestor.
It started with a small cardboard box labeled "D 20". Their contents: some primeval little bones, picked together from a tailings dump of lime mining in South Africa's Sterkfontein Cave, fifty kilometers north-west of Johannesburg. But when the paleoanthropologist Ron Clarke rummaged through the box on September 6, 1994, he became skeptical: in front of him were not the remains of a predator, as had been assumed, but of a hominid.
Clarke identified the left foot of an australopithecine in the fossils - and that's where things got interesting. Because the little foot - nicknamed "Little Foot" - shared both human and animal characteristics: the protruding big toe indicated that the creature was once able to swing up trees like a monkey; the heel, in turn, suggested a human-like upright gait. Was it even a direct ancestor of mankind?
As more and more bones from site D 20 from the Silberberg Grotto of Sterkfontein Cave, all matching the same individual, appeared in the holdings of the Johannesburg University of the Witwatersrand, Clarke ventured to prophesy that even more here fetch On July 3, 1997, Clarke's assistants actually found a shin that matched the foot in the cave. Gradually, 25 meters below the cave floor, an almost complete hominid skeleton, 130 centimeters in size, came to light, which was to become the subject of anthropological controversy under the catalog number StW 573.
Because the hominid proved to be a stubborn fellow. So it remains unclear to this day who it is actually about. It is believed that a representative of Australopithecus africanus found his last resting place here - the species first described by the South African anatomist Raymond Dart in 1925 as a non-Homo pre-human and estimated to have arrived on earth three to two million years ago walked.
However, precise dating is essential for reliable identification of the species - and this proved to be difficult with "Little Foot". Because the skeleton was embedded in cave rock that had baked into a breccia, it was not possible to assign it to clear layers. Clarke estimated the age at three to three and a half million years - but this was contradicted by Timothy Partridge, who also does research at the University of the Witwatersrand.
Together with his colleagues, Partridge radiodated the elements aluminum and beryllium in the surrounding quartz rock in 2003 and came to a surprising conclusion: "There's still a lot of work waiting for us here"
(Timothy Partridge) Not three, but more than four million years ago "Little Foot" is said to have taken its last step. So it either didn't belong to A. africanus, or the species is much older than previously assumed.
The geoscientists Joanne Walker and Robert Cliff from the University of Leeds, together with the archaeologist Alfred Latham from the University of Liverpool, have now ventured a new approach. The British researchers also relied on radiological dating, but chose the elements uranium and lead instead of aluminum and beryllium, which they isolated from the stalactites of the grotto. The principle is similar: the isotope uranium-238 decays to lead-206 with a half-life of 4.5 billion years; the age of a sample can be estimated from the ratio of the two isotopes.
The result: 2.2 million years. StW 573 would therefore not be older, but actually much younger than previously assumed. As a direct human ancestor, this half-ape-half-human being should therefore be eliminated, since by that time the genus Homo was already roaming the African lands.
"You've got it!" enthuses Paul Renne of the Berkeley Geochronology Center. "This is the most reliable dating of Little Foot yet."
Timothy Partridge sees it a little differently, of course. Because if the dating is correct, Little Foot is even a little younger than the famous fossil "Mrs. Ples" - a 2.5 million year old, mind you, male A. africanus, which was discovered in 1947 by the Scottish doctor and amateur paleontologist Robert Broom in the Sterkfontein Cave was discovered. However, animal bones found with Mrs. Ples appear younger than those found at Little Foot.
Partridge therefore remains skeptical: "There's still a lot of work to be done here."
