A new dating from a Sterkfontein cave in South Africa, northwest of Johannesburg, has given fossils of Australopithecus africanus, one of the species of Australopithecines, those predecessors of the human race.

Among them, the fossil of "Madame Ples", one of the first complete skulls of this genus of hominins, discovered in 1947 on this site full of calcite caves, which yielded several thousand fossils, including 500 of Australopithecines, inscribed by Unesco as a World Heritage Site under the name of "Cradle of Humanity".

The area housing "Mrs. Ples" had previously been dated to between 2.1 and 2.6 million years old, based on the age of sediments that fell into the cave after it was formed.

But "chronologically, it didn't fit", remembers Laurent Bruxelles, CNRS researcher, one of the authors of the study published this week in the journal PNAS.

"It was weird to see Australopithecines persisting for so long", explains this geologist to AFP: at 2.2 million years old, Homo habilis (first representative of the genus Homo) had already appeared in the region.

However, no trace of him, or of his tools, at this level of the cave.

"Little Foot's Little Sister"

Another disturbing fact: the emblematic skeleton of Little Foot, an even older Australopithecus found deep in the cave, and which recent research had just dated to 3.67 million years ago... The time gap with its "little sister" Mrs. Ples was too tall in view of the thickness of the sedimentary layers separating them.

The skeleton of "Little Foot", "big brother" of Ms. Ples, discovered at the Sterkfontein site in South Africa MUJAHID SAFODIEN AFP / Archives

Together with the South African paleontologist Ronald Clarke, lead author of the study, Laurent Bruxelles decided to use the same dating method as that of Little Foot.

Australopithecus fossils being too old to be dated directly with carbon 14, we can only date the sediments in which they are taken.

Dating by "cosmogenic isotopes" (cosmic rays that bombard the Earth) makes it possible to do in geological lace, by reconstructing as closely as possible the history of the cave, which has filled over time like an hourglass.

As with Little Foot, analyzes showed that the rocks in the cave had been buried with the fossils 3.4 to 3.6 million years ago.

And that the "intrusive" sediments - the layer of calcite which gave rise to the initial dating - had been put in place a million years later.

This revelation makes Australopithecus africanus a contemporary of Australopithecus afarensis from East Africa, the species of the famous Lucy discovered in 1974 in the Ethiopian Rift.

Chapel Quarrels

Two "synchronous" species living 4,000 kilometers from each other, and very much alike.

"The first australopithecines of the species of Little Foot were quite massive, when Lucy and Mrs. Ples are more slender", describes Laurent Bruxelles.

Are we dealing with the same species?

"We will never be able to prove that they were interfertile. But on the scale of millions of years, at only 4,000 km away, these species had plenty of time to move, to interbreed... so we can largely imagine a common evolution on the scale of all of Africa", according to this cave expert.

With the dating of Little Foot (older than Lucy) there were quarrels over the location of the cradle of humanity, in the East or in the South of the African continent.

By revealing these new parallel destinies, this latest study invites us to consider, once again, this notion on a continental scale.

The excavations of the Sterkfontein site - far from having revealed all its secrets - confirm that the tree of human evolution is more "bushy than linear", comments the French geologist, quoting Yves Coppens, the famous paleontologist died last week at 87.

The co-discoverer of Lucy had "understood the pan-African side of evolution for a long time", greets Laurent Brussels.

© 2022 AFP