The fossils of our earliest ancestors found in South Africa are a million years older than previously thought, meaning they walked the earth around the same time as their East African relatives like the famous ‘Lucy’, new research finds.
The Sterkfontein Caves at the Cradle of Humankind World Heritage Site southwest of Johannesburg have yielded more Australopithecus fossils than any other site in the world.
Among them was “Mrs Ples”, the most complete skull of an Australopithecus africanus found in South Africa in 1947.
Based on previous measurements, Mrs. Ples and other fossils found at a similar depth in the cave have been estimated to be between 2.1 and 2.6 million years old.
But “chronologically it didn’t fit,” said French scientist Laurent Bruxelles, one of the authors of a study published in the scientific journal PNAS on Monday.
“It was bizarre to see some Australopithecus surviving for so long,” the geologist told AFP.
Around 2.2 million years ago, Homo habilis – the earliest species of the genus Homo, which also includes Homo sapiens – roamed the region.
But deep in the cave where Ms. Ples was found, there were no signs of Homo habilis.
– ‘Contemporaries’ –
Doubts about Ms Ples’ age were also raised by recent research showing that the nearly complete skeleton of an Australopithecus known as “Little Foot” was 3.67 million years old.
Such a large age difference between Mrs. Ples and Little Foot seemed unlikely, since they were separated by so few layers of sediment.
Because the fossils are too old and fragile to test, scientists are analyzing the sediment near where they were found.
The earlier data underestimated the age of the fossils because they measured calcite riverstone mineral deposits that were younger than the rest of this cave section, the study says.
For the latest study, the researchers used a technique called cosmogenic nuclide dating, which looked at the concentrations of rare isotopes that are formed when rocks containing quartz are struck by high-velocity particles coming from space.
“Their radioactive decay dates to when the rocks were buried in the cave when they fell into the entrance along with the fossils,” said the study’s lead author Darryl Granger of Purdue University in the US.
The researchers found that Ms. Ples and other fossils in her vicinity were between 3.4 and 3.7 million years old.
That means members of Australopithecus africanus like Ms. Ples were “contemporaries” of East Africa’s Australopithecus afarensis, including the 3.2-million-year-old Lucy found in Ethiopia, said Dominic Stratford, research leader of the caves and one of the study’s authors.
– Our family tree ‘more like a bush’ –
It could also potentially change our understanding of our ancestral history.
South Africa’s Australopithecus was previously thought to be “too young” to be the ancestor of the genus Homo, Stratford said. This meant that Lucy’s homeland in East Africa was considered the more likely place where the genus Homo had evolved.
But the new research shows that South Africa’s Australopithecus had almost a million years to evolve into our homo ancestor.
Or they could have worked on it together.
“Over a period of millions of years, just 4,000 kilometers (2,500 miles) apart, these species have had plenty of time to travel, to breed with each other… so we can broadly envision common evolution across Africa,” Bruxelles said.
Research has shown that hominid history is “more complex than linear evolution,” he added.
Our family tree is actually “more like a bush, to use the words of our late friend Yves Coppens,” Bruxelles said, referring to the French paleontologist credited with co-discovery of Lucy. Coppens died last week.
“He had long understood the pan-African nature of evolution,” Bruxelles said.
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