The fossils of the earliest human 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,” according to new research.
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 of the cave were estimated to be between 2.1 and 2.6 million years old.
However, “chronologically that didn’t fit,” said French scientist Laurent Bruxelles, one of the authors of a study published on Monday in the PNAS science journal.
“It was bizarre to see some Australopithecus lasting for such a long time,” the geologist told AFP.
Around 2.2 million years ago, the Homo habilis, the earliest species of the Homo genus that includes Homo sapiens, was already roaming the region.
But there were no signs of Homo habilis at the depth of the cave where Mrs. Ples was found.
Also casting doubt on Mrs. Ples’s age was recent research proving that the almost-complete skeleton of an Australopithecus known as “Little Foot” was 3.67 million years old.
Such a big gap in ages between Mrs. Ples and Little Foot seemed unlikely given that they were separated by such few sedimentary layers.
Because the fossils are too old and fragile to test, scientists analyze the sediment near where they were found.
Previous dates underestimated the age of the fossils because they measured calcite flowstone mineral deposits, which were younger than the rest of that cave section, the study concluded.
For the latest study, the researchers used a technique called cosmogenic nuclide dating, which analyzed levels of rare isotopes created when rocks containing quartz were hit by high-speed particles that arrived from outer space.
“Their radioactive decay dates when the rocks were buried in the cave [and…] fell in the entrance together with the fossils,” said the study’s lead author, Darryl Granger of Purdue University in the US.
Researchers found that Mrs. Ples and other fossils in her vicinity were between 3.4 and 3.7 million years old.
Human ancestors in South Africa around 3.2-million-year-old
This means that members of Australopithecus africanus like Mrs. Ples were “contemporaries” of East Africa’s Australopithecus afarensis, including 3.2-million-year-old Lucy who was found in Ethiopia, said Dominic Stratford, director of research at the caves and one of the study’s authors.
It could also possibly alter our understanding of our ancestral history, AFP says.
The South African Australopithecus had previously been considered “too young” to be the ancestor of the Homo genus, Stratford said. That meant that Lucy’s home of East Africa was thought to be the most likely place where the Homo genus evolved.
The new research, however, shows that the South African Australopithecus had had almost a million years to evolve into our Homo ancestor. Alternatively, of course, they could have worked on it together.