A picture taken in 2002 shows "Little Foot," an almost complete hominid skeleton in a rock at the Sterkfontein Caves, some 40 kms north of Johanneburg. "Little Foot" is far younger than initially thought, a new study says. [Photo: AFP/POOL/File/Yoav Lemmer]

A key fossil found at South Africa's Sterkfontein Cave, a site dubbed "the Cradle of Humankind" for its trove of hominid relics, is far younger than initially thought, a new study says.

"Little Foot," a fossil with both ape-like and human features, was found in the 1990s thanks to remarkable luck and diligent work.

It was first dated to between 3.0 and 3.5 million years old, and later to more than 4.1 million years.

Those dates generated huge excitement.

For one thing, they threw up a South African contemporary to "Lucy," the famous Australopithecus afarensis fossil found in Ethiopia's Awash Valley in 1974 and, until then, chief contender for the title of ancestor of mankind.

But a paper published in the US journal Science on Thursday says Little Foot's age is likely to be around 2.2 million years. If so, rather than being man's direct ancestor, Little Foot is more likely to have been a distant cousin.

The dating method is based on a measurement of an isotope of lead, Pb 206, derived from the decay of uranium 238, on layers of rock above and below the fossil. The more lead in the sample, the older the rock.

Sterkfontein, located 50 kilometers (30 miles) north of Johannesburg, has produced about a third of the world's known early hominid fossils.

Little Foot leapt into the headlines thanks to South African paleoanthropologist Ronald Clarke.

In 1994, Clarke spotted four left-foot hominid bones as he sifted through bags of fossilised animal bones that had been dumped after a mine blast, decades earlier, at a large cavern within the cave system.

He attributed them to the hominid genus Australopithecus, and, because the bones were relatively small, the specimen was dubbed "Little Foot."

Clarke spent the next few years exhaustively going through other bags of the fossils, and eventually found further foot bones from the same individual.

That prompted a search for further remains in the grotto which, even more remarkably, yielded the bones' owner -- a nearly complete skeleton, cemented in a tough sedimentary rock called breccia, which has been gently excavated ever since.

Debate has always swirled around the dating of Little Foot, with paleontologists jousting over the age of sedimentary layers, the remains of fauna found within them and residual magnetic polarity found in ancient rock.

Fixing a date is important for anthropology, not just for glory and tourist revenue.

One of the big questions about the rise of mankind is when, exactly, our ancestors began walking upright and started to use tools.

The first recognisable stone implements appeared in Africa around 2.6 million years ago, and the toolmaker is believed to be Homo habilis, whose evolution -- apparently from a species of Australopithecus -- is considered by some to have led directly to man.

Little Foot is not the only famous denizen of Sterkfontein to be redated.

"Mrs. Ples," a nearly complete australopithecene skull found in 1947, "is now considered to lie within (the range of) 2.15-2.14 million" years old, the study said.

Other estimates have put Mrs. Ples at 2.5 million years of age, or more.

Lead authors in the new study are Jo Walker and Bob Cliff of the School of Earth and Environment at the University of Leeds, northern England.

Cliff, in an interview with AFP, said that the earlier dating of Little Foot itself posed a conundrum.

It raised questions as to this genus' place in the hominid tree, if smarter hominids had split from Australopithecus many hundreds of thousands of years before.

Cliff acknowledged that the dating issue would remain a matter of heated debate, as paleontological pride and prestige were involved. "It's going to be controversial," he said.