The skull of 'Little Foot', Australopithecus prometheus, from south Africa, now believed to be a contemporary of 'Lucy', Au. Afarensis, from Ethiopia.
As I have pointed out many times here and on the social media, as well as in my popular book, What Makes You So Special: From The Big Bang to You., far from the often repeated creationist lie that there are no transitional fossils, there are actually so many of them that they serve only to cloud, not clarify the picture. Just when you think there is a nice direct line from a species of Australopithecus up to say, Homo erectus and thence to us, up pops another Australopithecus that might be a side branch or it might be an early ancestor of Homo sapiens. In the end we are left with a confusing collection of ancient African fossils that might or might not be our direct ancestors or might or might not be the ancestors of am extinct side branch, with no real way to determine which.
The picture is confused further when the fossils from which DNA has been extracted show that early hominins had a tendency to spread over a very wide range, evolve for a while in isolation, but not enough to be incapable of interbreeding with a cousin species, then come back together again and exchange DNA by interbreeding, so we may in fact never have had a single original distinct ancestral species but we are the descendants of two or more that hybridized.
Now the picture has been clarified a little by a scientists from Purdue University, West Lafayette, Indiana, USA, the University of the Witwatersrand, Johannesburg, South Africa, and the University Toulouse Jean Jaurès, Toulouse, France, who have used a new dating method developed by Dr Darryl Granger of Purdue University to reassess the date of several hominin fossils found in the Sterkfontein Caves, South Africa and pushed their dates back more than a million years. This makes them older that 'Lucy' (Au. afarensis) who is believed to be close to our direct Australopithecine ancestor, if not actually our ancestor. It is hoped, that more accurate dating will leader to a more accurate placing of these fossils over time, so making lineages easier to identify.
From the Purdue University news release:
For decades, scientists have studied these fossils of early human ancestors and their long-lost relatives. Now, a dating method developed by a Purdue University geologist just pushed the age of some of these fossils found at the site of Sterkfontein Caves back more than a million years. This would make them older than Dinkinesh, also called Lucy, the world’s most famous Australopithecus fossil. The “Cradle of Humankind” is a UNESCO World Heritage Site in South Africa that comprises a variety of fossil-bearing cave deposits, including at Sterkfontein Caves. Sterkfontein was made famous by the discovery of the first adult Australopithecus, an ancient hominin, in 1936. Hominins includes humans and our ancestral relatives, but not the other great apes. Since then, hundreds of Australopithecus fossils have been found there, including the well-known Mrs. Ples, and the nearly complete skeleton known as Little Foot. Paleoanthropologists and other scientists have studied Sterkfontein and other cave sites in the Cradle of Humankind for decades to shed light on human and environmental evolution over the past 4 million years.Dr Granger's speciality is in dating cave sediments using a technique he developed as a PhD student. His method is now the standard dating technique for dating archaeological finds in caves. His previous work at Sterkfontein dated the Little Foot skeleton to about 3.7 million years old, although the age of other fossils at the site is still a subject for debate.
In a study published in the Proceedings of the National Academy of Sciences, Granger and a team of scientists including researchers from the University of the Witwatersrand in Johannesburg, South Africa and the University Toulouse Jean Jaurès in France, have discovered that not only Little Foot, but all of the Australopithecus-bearing cave sediments date from about 3.4 to 3.7 million years old, rather than 2-2.5 million years old as scientists previously theorized. That age places these fossils toward the beginning of the Australopithecus era, rather than near the end. Dinkinesh [Lucy, in the Ethiopian language, Amharic (for 'You are marvellous')], who hails from Ethiopia, is 3.2 million years old, and her species, Australopithecus africanus, hails back to about 3.9 million years old.More technical detail is given in the abstract to the team's open access paper in PNAS:
Sterkfontein is a deep and complex cave system that preserves a long history of hominin occupation of the area. Understanding the dates of the fossils here can be tricky, as rocks and bones tumbled to the bottom of a deep hole in the ground, and there are few ways to date cave sediments.
In East Africa, where many hominin fossils have been found, the Great Rift Valley volcanoes lay down layers of ash that can be dated. Researchers use those layers to estimate how old a fossil is. In South Africa – especially in a cave – the scientists don’t have that luxury. They typically use other animal fossils found around the bones to estimate their age or calcite flowstone deposited in the cave. But bones can shift in the cave, and young flowstone can be deposited in old sediment, making those methods potentially incorrect. A more accurate method is to date the actual rocks in which the fossils were found. The concrete-like matrix that embeds the fossil, called breccia, is the material Granger and his team analyze.
Granger and the team used accelerator mass spectrometry to measure radioactive nuclides in the rocks, as well as geologic mapping and an intimate understanding of how cave sediments accumulate to determine the age of the Australopithecus-bearing sediments at Sterkfontein.Sterkfontein has more Australopithecus fossils than anywhere else in the world, but it’s hard to get a good date on them. People have looked at the animal fossils found near them and compared the ages of cave features like flowstones and gotten a range of different dates. What our data does is resolve these controversies. It shows that these fossils are old – much older than we originally thought.
What I hope is that this convinces people that this dating method gives reliable result. Using this method, we can more accurately place ancient humans and their relatives in the correct time periods, in Africa, and elsewhere across the world.
Dr Daryl Granger, lead author
Department of Earth, Atmospheric, and Planetary Sciences
Purdue University, West Lafayette, IN, USA
Granger and the research group at the Purdue Rare Isotope Measurement Laboratory (PRIME Lab) study so-called cosmogenic nuclides and what they can reveal about the history of fossils, geological features and rock. Cosmogenic nuclides are extremely rare isotopes produced by cosmic rays —high-energy particles that constantly bombard the earth. These incoming cosmic rays have enough energy to cause nuclear reactions inside rocks at the ground surface, creating new, radioactive isotopes within the mineral crystals. An example is aluminum-26: aluminum that is missing a neutron and slowly decays to turn into magnesium over a period of millions of years. Since aluminum-26 is formed when a rock is exposed at the surface, but not after it has been deeply buried in a cave, PRIME lab researchers can date cave sediments (and the fossils within them) by measuring levels of aluminum-26 in tandem with another cosmogenic nuclide, beryllium-10.
In addition to the new dates at Sterkfontein based on cosmogenic nuclides, the research team made careful maps of the cave deposits and showed how animal fossils of different ages would have been mixed together during excavations in the 1930s and 1940s, leading to decades of confusion with the previous ages.
The age of the fossils matters because it influences scientists’ understanding of the living landscape of the time. How and where humans evolved, how they fit into the ecosystem, and who their closest relatives are and were, are pressing and complex questions. Putting the fossils at Sterkfontein into their proper context is one step towards solving the entire puzzle.
Significance
Australopithecus fossils from the richest hominin-bearing deposit (Member 4) at Sterkfontein in South Africa are considerably older than previously argued by some and are contemporary with Australopithecus afarensis in East Africa. Our dates demonstrate the limitations of the widely accepted concept that Australopithecus africanus, which is well represented at Sterkfontein, descended from A. afarensis. The contemporaneity of the two species now suggests that a more complex family tree prevailed early in the human evolutionary process. The dates highlight the limitations of faunal age estimates previously relied upon for the South African sites. They further demonstrate the importance of detailed stratigraphic analysis in assessments of accurate dating of the karst cave sites in South Africa, which are stratigraphically highly complex.
Abstract
Sterkfontein is the most prolific single source of Australopithecus fossils, the vast majority of which were recovered from Member 4, a cave breccia now exposed by erosion and weathering at the landscape surface. A few other Australopithecus fossils, including the StW 573 skeleton, come from subterranean deposits [T. C. Partridge et al., Science 300, 607–612 (2003); R. J. Clarke, K. Kuman, J. Hum. Evol. 134, 102634 (2019)]. Here, we report a cosmogenic nuclide isochron burial date of 3.41 ± 0.11 million years (My) within the lower middle part of Member 4, and simple burial dates of 3.49 ± 0.19 My in the upper middle part of Member 4 and 3.61 ± 0.09 My in Jacovec Cavern. Together with a previously published isochron burial date of 3.67 ± 0.16 My for StW 573 [D. E. Granger et al., Nature 522, 85–88 (2015)], these results place nearly the entire Australopithecus assemblage at Sterkfontein in the mid-Pliocene, contemporaneous with Australopithecus afarensis in East Africa. Our ages for the fossil-bearing breccia in Member 4 are considerably older than the previous ages of ca. 2.1 to 2.6 My interpreted from flowstones associated with the same deposit. We show that these previously dated flowstones are stratigraphically intrusive within Member 4 and that they therefore underestimate the true age of the fossils.
Granger, Darryl E.; Stratford, Dominic; Bruxelles, Laurent; Gibbon, Ryan J.; Clarke, Ronald J.; Kuman, Kathleen
Cosmogenic nuclide dating of Australopithecus at Sterkfontein, South Africa
Proceedings of the National Academy of Sciences (PNAS) 2022 119(27) e2123516119; DOI: 10.1073/pnas.2123516119
Copyright: © 2022 The authors.
Published by PNAS. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Although placing these fossils in the right order, stratigraphically, this also highlights what I said above - the early hominins spread widely across their range in Africa and began to speciate, as these two contemporaneous species show. However, it also means the probability of them coming back together again and interbreeding later has to be taken into account, so making our origins more complicated rather than simplifying things.
For a Bible-literalist creationist, this sort of information is a disaster as it shows their primitive origin myths have absolutely no basis in fact, not even allegorical fact, and the idea of a single founder couple from just a few thousand years ago is even more ridiculous and untenable. Again, we see creationism utterly refuted by the simple expedient of revealing the truth.
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