The Age of Little Foot

Scientists continue the debate surrounding the true age of the famous fossil skeleton discovered at Sterkfontein Caves in South Africa.

In April of 2015, National Geographic published an article entitled ‘Little Foot’ Fossil Skeleton Rivals Famous Lucy in Age. Widely read, it was one of many articles published by the media following a 2015 scientific report in Nature which concluded that the fossil skeleton, discovered at Sterkfontein in South Africa nearly two decades before, was more than 3.6 million years old, confirming some earlier conclusions by previous studies made soon after the skeleton’s discovery in the late 1990’s. This new report, said some scholars, finally put the lid on an ongoing debate with far-reaching implications for human evolution — like which hominin species was older — the famous ‘Lucy’ species, Australopithecus afarensis, fossil remains of which were discovered by Donald Johanson in 1974 in the Hadar region of Ethiopia, East Africa — or the ‘Little Foot’ species, discovered by Ron Clarke and his colleagues in the Sterkfontein Caves in South Africa in the 1990’s, two decades later. The study’s results supported the needle angling toward Southern Africa as the possible ‘birthplace’ of humanity, rather than East Africa, where many scholars currently suggest was humanity’s cradle.  

Time to finally move on. Southern Africa could be the place.  

But not so fast, says Jan Kramers of the University of Johannesburg. He contends that there is still more work to do before closing the book on the debate. There is, he says, “a need for the discussion to go on, and then for more analytical work.” He can say this because, more recently, he and Paul Dirks (James Cook University, Australia) conducted a study that may provide new fodder that could eventually pop the balloon that emerged from the 2015 Nature report. It revolved around pieces of chert. 

But the whole story about what Little Foot is, and the age, began about 20 years ago.

The Discovery

Many archaeologists and paleontologists would tell us that not all discoveries are first recognized in the field. Some, in fact, come from boxes secured in the backrooms of labs and museums, long after the artifacts or fossils have been recovered from the sites. Such was the case with Ron Clarke at the University of Witwatersrand, when, in 1994, he came across four humanlike left foot bones while searching through boxes containing fossil fragments. Identifying them as likely belonging to a hominin, he determined that they were from the same individual, a rather remarkable find. The bones had actually originally been recovered in 1980 and were within a mix of other mammal fossil bones recovered from the Silberberg Grotto, a cavern within the (by now) famous Sterkfontein cave system. A bit like a needle in a haystack, a hominin fossil find can be easily lost within the plethora of other mammal finds in a collection or site, so it was not altogether surprising that they were missed more than a decade earlier.

littlefootfootbonesThe foot bones displayed characteristics both human and ape-like, and were designated as belonging to the Australopithecus genus, catalogued as Stw 573. Clarke and Professor Phillip Tobias announced the discovery in 1995, nick-naming it “Little Foot”, due to the diminutive nature of the bones as compared to the same for modern humans. Right: Footbones of Little Foot.  Drawn remake from “Science” on 28 July 1995, Tobias Fluegel, Wikimedia Commons.

Clarke’s adventure with Little Foot didn’t stop here. In 1997, while searching through more boxes of fossils from Sterkfontein, Clarke found and identified another eight leg and foot bones — again, according to Clarke, from the same individual. He noticed that one of the specimens, a shin bone, had a clean break, a typical feature on fossil bones that can be created by blasting by miners in caves. Suspecting that there were more where these came from within the Grotto, he asked two of his assistant preparators, Stephen Motsumi and Nkwane Molefe, to go search for the matching piece likely left behind in the cave and possibly still exposed in the breccia of the cave, hopefully thus leading to the rest of the skeleton. Taking a cast of the broken shin bone and hand-held lamps, they conducted a painstaking search within the darkness of the Grotto. Two days of work yielded the result they had hoped for, followed by further excavations and more bones, including the left side of a complete skull. In the following years, Clarke and his assistants, using hammers and small chisels, eventually uncovered a relatively complete, articulated skeleton, more complete than the famous “Lucy” Australopithecus afarensis skeleton discovered decades before by Donald Johanson at Hadar, Ethiopia. 

It had taken 15 years. But the results were nothing less than remarkable. It is to date one of the most complete, articulated Australopithecus fossil skeletons ever found, unaffected by the acts of predators post mortem. 

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 The Sterkfontein caves, wherein the Silberberg Grotto, the location where Little Foot was found, is located. Mike Peel, Wikimedia Commons

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 Entrance to the cave/grotto where Little Foot was discovered. Mike Peel, Wikimedia Commons

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 Little Foot’s foot bones. Mike Peel, Wikimedia Commons

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 General view of Little Foot skeleton in its original position in Sterkfontein cave, November 2006. Text and image V. Mourre, Wikimedia Commons

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 Detailed view of part of the remains of Little Foot in situ in the Silberberg Grotto in 2006. V. Mourre, Wikimedia Commons

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The Million Dollar Questions

The most tantalizing issue of the discovery, however, revolves around two questions, still being debated to this day: What kind of Australopithecus is Little Foot and how old is the skeleton? The answers to those questions could significantly impact our picture of human evolution in Africa in terms of the origins of our genus and species.  

In 1995, soon after the initial bones of Little Foot had been discovered, Clarke and colleagues determined that the finds likely belonged to Australopithecus. But once elements of the skull emerged sufficiently enough for reasonable examination, he could see a combination of features that clearly could not fit neatly into either Australopithecus africanus, the best known species found at Sterkfontein and other locations in South Africa,and Australopithecus afarensis, the other well-known Australopithecine, remains of which have been found primarily in East Africa. Nor can it be lumped with the more recently discovered Australopithecus sediba, the nearly two-million-year-old species discovered by the University of Witwatersrand’s Lee Berger at the South African Malapa caves site. But key morphological features of Little Foot, according to Clarke, did seem to match corresponding characteristics found in other specimens found at Makapansgat and Sterkfontein, which have been assigned to a “second species” of South African Australopithecus sometimes referred to as Australopithecus prometheus, a species first penned by Raymond Dart in the 1940’s with the discovery of fossil remains at Makapansgat, but which has since the 1960’s been lumped into the africanus species.

Thus, until further study and fossil finds can shed more light on the issue, the debate on species assignment for Little Foot continues to this day, complicated by the fact that “there is no authoritative description of the fossil published yet, made difficult by the fact that many of the bones, including the skull, are apparently badly crushed and difficult to reconstruct,” says Kramers, who conducted a recent dating study of the Little Foot sediments of the Grotto. 

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 Professor Ron Clarke from Wits University with the skull of Little Foot (StW 573). Text and image Wits University, Wikimedia Commons

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 Little Foot complete skull. Wits University, Wikimedia Commons

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Dating Little Foot

Equally perplexing has been the question of age. The initial discovery and study of Little Foot, when most of the fossil skeleton still remained embedded in its breccia matrix within the Grotto, yielded a a date range of between 3.0 and 3.5 million years old. It was a sensational report, and Little Foot was touted by the discoverers as the oldest known hominin in South Africa, rivaling Lucy (Au. afarensis) as the oldest known Australopithecine. But that date range met fierce scholarly criticism, with a number of scholars suggesting that the range was too old. Two later studies suggested a younger age, significantly less than 3 million, one study suggesting 2.2 million years based on dating of the flowstone surrounding Little Foot’s remains. 

But two more recent studies, one reported in 2014 and the other in 2015, pushed the clock back again on Little Foot’s age. In the 2014 study report, lead author Laurent Bruxelles and colleagues maintained that the stratigraphic context of the Little Foot remains is more complex than previously thought. They suggested based on their analysis that post-depositional processes created voids in the breccia surrounding the skeleton. The voids were subsequently filled in by flowstone growth, the element that was dated by other researchers who concluded the later age range for Little Foot. This, according to the 2014 study report authors,  “demonstrates that the proposed dates based on the flowstone deposition can give only a minimum age for StW 573 and that the flowstone formation came after, and probably long after, the breccia deposition.” Considering the hundreds of thousands of years it would take for the flowstone fillings to develop, maintain the report authors, Little Foot, embedded in the breccia that was surrounded by the flowstone, had to be significantly older than 2.2 million years.* They suggested an age of about 3 million years. Further buttressing the earlier chronology, the 2015 Nature study report**, led by Darryl E. Granger of Purdue University, used new radioisotopic techniques to “show that the breccia containing StW 573 did not undergo significant reworking, and that it was deposited 3.67±0.16million years ago, far earlier than the 2.2 million year flowstones found within it.”** From this flowed the before-mentioned National Geographic article and a flurry of other media reports in 2015, with some scholars suggesting that perhaps the debate on Little Foot’s age was finally over. 

Dating the Chert

But scientific inquiry is a never-ending pursuit. Enter a new study conducted by Jan D. Kramers of the University of Johannesburg and Paul H.G.M. Dirks of James Cook University, the paper from which was published in 2017 in the South African Journal of Science. With the results of this study, one could argue that we need to stop the press on the issue of Little Foot’s age. Reflecting the perspectives of some scholars, Kramers and Dirks felt that the age issue needed to be revisited. Two main reasons or questions underpinned their rationale. “The older age would potentially make Little Foot an alternative ancestor [to Lucy, or Au. afarensis] and in the eyes of many paleoanthropologists that does not fit with its apparently derived features, particularly dentition,” stated Kramers. “Second,” Kramers continued, “the 3.67±0.16 Myr age is more than a million years older than any other hominin fossil found in the Cradle of Humankind, and this problem is not limited to hominins. In faunal studies it appears that several species otherwise known only from fossil deposits dated at less than 2.5 Myr would have made their first appearance in this site, to then disappear again for more than a million years before re-emerging.” To accept the earlier dating without question, says Kramers and Dirks, still makes Little Foot’s place in human evolution, based on current knowledge, “very puzzling, and even confusing”.

Kramers and Dirks thus re-examined the data already used and analyzed by the Granger et al. study, focusing on a more detailed analysis of chert samples found in the breccia mix. Applying data from the same radiometric dating techniques used in the Granger study, they found that two of the chert fragment samples “could not have been together in the same sediment underground for longer than 2.8 million years” — a maximum age that therefore applies to the sediments encasing Little Foot, and opening up further discussion and study on the Little Foot case. 

If what Kramers and Dirks is suggesting is true, what then accounts for the disparate dates within the sediment encasing Little Foot? Is Little Foot at most 2.8 million years old, or 3.67, a difference of nearly a million years?

A Second Cave Chamber?

Kramers and Dirks suggests the possibility of a second chamber, which once existed just above the chamber in which Little Foot was found, as an explanation for the disparity. “The only way to reconcile the results is to postulate that there was a cave chamber above the present-day Silberberg Grotto at around 2.8 Myr, which contained sediment that already had been there, underground, for up to a million years,” writes Kramers. “Further, there had to have been an opening that was a death trap as well as a conduit for sediment. A huge tilted block currently lying at the surface above the Silberberg Grotto is a strong indication that such a chamber existed.”****

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Above: Prominent surface feature at Sterkfontein and its relation to the Silberberg Grotto. (a) Cave map showing the position of surface workings, entry chambers and (b) relative to the Silberberg Grotto. (b) View from the east of a large tilted dolomite block on the south side of the open excavation, adjoining breccia of Member 4. Source: Adapted from Martini et al.41; (b) Photo: Paul Dirks 

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But Clarke and his research team dispute this, saying that “an upper chamber could not have existed and contributed deposit through several meters of underlying breccia and flowstone,” based on their years of careful analysis of the geomorphology and sediment deposits of the cave system, asserting that there is no evidence that an upper chamber ever existed. 

“They are allowing their assumption of an upper chamber to dictate their dating model,” writes Clarke.****

Moreover, the dating specialist for the 2015 study, Darryl Granger, also strongly disputes Kramer and Dirks’ methodology in their study, suggesting that they downplayed the isochron dating used in the 2015 study and simply focused on a few samples of chert, then projecting from that evidence that other sediments may have been reworked from a deposit originating from a phantom upper cave.

Clarke and colleagues detail their response to the Kramers and Dirks study in a paper published in the South African Journal of Science.

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Re-opening the Discussion

But Kramers offers no finality to his recent study, and neither should the Granger, et al. study be considered the final word, he maintains. Kramers and Dirks’ date is well within the generally accepted date range currently assigned to Australopithecus africanus, the Australopithecine that seems to have been prevalent in South Africa. Moreover, “this should be looked at as work in progress,” says Kramers, referring to his study, “and in particular, an attempt to get the discussion on the age of the Little Foot fossil going again…….so far our 2.8 maximum age is still based on a few samples only. There is a need for the discussion to go on. This should go hand in hand with a full published description of the fossil, now possible because it has been completely excavated. Because of the lack of a description we don’t know on what basis Clarke has claimed the fossil to be A. prometheus, which otherwise does not exist [in the currently generally accepted species lexicon]. It is quite urgent to have that description well published so that we know WHAT we place WHERE in the hominin family tree.”

Herein lies the rub of scientific inquiry in the search for truth. What is true today may not necessarily be true tomorrow, as seemingly irrefutable evidence and conclusions can be overturned — and back again — at any point in the future by additional study and new technological and methodological developments. So is the truth about Little Foot’s age really now set in stone, as Granger, et al. would suggest? Perhaps yes. Or, as science’s inexorable search for the facts have proven over and over again in the past—maybe not. 

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*L. Bruxelles et al., Stratigraphic analysis of the Sterkfontein StW 573 Australopithecus skeleton and implications for its age, Journal of Human Evolution 70 (2014) 36 – 48

**Darryl E. Granger, et al., New cosmogenic burial ages for Sterkfontein Member 2 Australopithecus and Member 5 Oldowan, Nature vol. 522, 4 June 2015 

***Kramers JD, Dirks PHGM. The age of fossil StW573 (‘Little Foot’): An alternative interpretation of 26Al/10Be burial data. S Afr J Sci. 2017;113(3/4), Art. #2016-0085, 8 pages. http://dx.doi.org/10.17159/ sajs.2017/20160085 

**** http://www.maropeng.co.za/news/entry/the-truth-about-little-foot#disqus_thread

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