South African hominids were contemporaries of the Afars and some other middle Pliocene australopithecines: they lived in the cradle of humanity 3.4 to 3.7 million years ago, not 2.07 to 2.61 million years ago , as previously thought.
Archaeologists have clarified the age of Australopithecuswhose fossilized remains were found at the site of Sterkfontein. Cosmogenic dating has shown that South African individuals lived 3.4 to 3.7 million years ago, and not 2.07 to 2.61 million years ago, as previously thought.
The revised age makes the South African hominins contemporaneous with the Afar and some other australopithecines from the middle Pliocene, which began 5.33 million years ago and ended 2.59 million years ago.
On the territory of the Republic of South Africa, not far from Johannesburg, there is a complex of monuments called Cradle of Humanitywhich is included in the list of UNESCO World Heritage Sites.
In an area of approximately 474 square kilometers there are many limestone caves that are rich in fossil remains. The complex includes such famous sites as Drimolen, Swartkrans, Kromdry, Dinaledi, Coopers and some others.
Fossilized remains have been found in them, in particular, of African Australopithecus (Australopithecus africanus), Australopithecus sediba (A. sediba), Paranthropus (P. robustus), Homo habilis (H. habilis), Ice man (H. naledi) and some other hominin species.
cradle of humanity
In the Sterkfontein monument is also located in the Cradle of Humankind, which is a complex of limestone caves.
The excavations of this monument began in 1936 and brought back a large collection of finds: at the end of the 20th century, more than 300 fossils were known that belonged to African australopithecines, the first Homo.
The most famous of these finds is the Sts-5 Australopithecus skull, found in 1947 and known as Mrs Ples.
Unlike most East African sites of such age, the Sterkfontein finds are difficult to date, because it contains no volcanic deposits that can be dated with reliable physical methods.
darrylgranger, of Purdue University, together with colleagues from France and South Africa, decided to clarify the age of the Sterkfontein finds. The results of their research are published in the journal Proceedings of the National Academy of Sciences (PNAS).
To further this study, they selected quartz samples from Sterkfontein for analysis using cosmogenic dating aluminum-26 and beryllium-10.
Cosmogenic dating is based on cosmic radiation from the Sun and from our galaxy, formed mainly by protons and, to a lesser extent, alpha particles, electrons and other particles, but above all by neutrons of extragalactic origin.
These particles are capable of passing through the high atmospheric layers, reaching the earth’s surface and interacting with some elements present in minerals and transforming their nuclei.
The statistical analysis of the presence of these cosmogenic nuclei on the most superficial part of the rocks has become an infallible method for knowing the exposure time of these surfaces and, therefore, of the geomorphological evolution of the earth’s surface.
Using this method, the archaeologists appreciated that most of the Australopithecus fossils found at Sterkfontein come from the M4 layer, whose upper and lower time limits are determined from the sintered stone age using uranium-lead and paleomagnetic methods. .
However, in the new work, the archaeologists concluded that calcite appeared in this layer much later than hominin bones.
As a result of the study, scientists found that the age of the deposits in the M4 layer is about 3.41 ± 0.11 million years. The sediment sample from Fossils Cave, where four Australopithecus fossils were found in 1937, turned out to be about the same: 3.49 ± 0.19 million years old.
Another date was obtained for Yakovets Cave, where the skull of StW-578 and several fragments of the postcranial skeleton were excavated. Taking into account the results of previous research, scientists estimated the age of the finds from this place at 3.61±0.09 million years.
The dates obtained for the M4 layer turned out to be much older than previously thought (around 2.61 to 2.07 million years). However, they are consistent with estimates of past ages for the Silberberg Grotto and Yakovets Cave.
The previous estimate of the age of the M4 layer remains was also confirmed by the discovery of two horse fossils (equus), which appeared in South Africa no earlier than 2.3 million years ago.
However, one of these bones, judging by reexamination, belonged to a member of the bovid family (Bovidae). The second apparently fell into the M4 layer of later deposits.
Archaeologists have concluded that all of the Australopithecus fossils found at Sterkfontein date from about 3.7 to 3.4 million years ago.
Thus, they were earlier members of the genus Australopithecus, and lived in the Middle Pliocene around the same time as other hominids, including Australopithecus afarensis (A. afarensis), Deyremeda Australopithecus (a. deyiremeda), flat-faced Kenyanthropus (Kenyanthropus platyops), Australopithecus bahrelghazali (A. bahrelghazali) and late Anaman Australopithecus (A.anamensis).
In South Africa, Sterkfontein’s Australopithecus lived about a million years before Paranthropusearly Homo, and that the Sediba Australopithecus.
Cosmogenic nuclide dating of Australopithecus at Sterkfontein, South Africa. Darryl E. Granger et al. PNAS, June 27, 2022, 119 (27) e2123516119. DOI:https://doi.org/10.1073/pnas.2123516119