Taung, 2.3 Million Years Ago – Scratched bones and fossil primate teeth as keys to a lost world

On December 23, 1924, the Australian anatomist Raymond Dart chipped away the last bit of rock encasing the skull of a small fossil primate. The specimen had been part of a collection of fossil scraps sent to him from a limestone quarry in Taung, South Africa – not too far from where he was teaching anatomy in Johannesburg’s University of Witwatersand – but it was unlike any prehistoric primate Dart had seen before. Even though the skull was clearly from a juvenile individual, Dart was still impressed with its flat face, human-like dentition, and large brain (the convolutions of which were preserved in a fossilized cast) – characteristics which hinted at its close relationship to our species. While most paleoanthropologists at the time thought that humans had evolved in Asia, Dart believed he had found evidence that Africa had been home to the earliest humans, and he rushed a paper to Nature describing this new creature. He called it Australopithecus africanus – the “southern ape from Africa” – and this first specimen became popularly known as the “Taung child.”

Dart was sure he had found a creature which closed the gap between apes and the first humans. His A. africanus was not “a caricature of precocious hominid failure”, as he appraised the famous “Pithecanthropus” (today known as Homo erectus), but was instead “a creature well advanced beyond modern anthropoids [i.e. great apes] in just those characters, facial and cerebral, which are to be anticipated in an extinct link between man and his simian ancestor.” Yet Dart went a step beyond this. At the time it was thought that prehistoric climates in South Africa had not changed very much since the time the last dinosaurs disappeared, and the fact that the fossil was found at a site along the margin of the harsh Kalahari Desert meant that this early human had lived in a very harsh environment. It was this landscape which had made us human, Dart argued, as the evolution of humans required “a more open veldt country where competition was keener between swiftness and stealth, and where adroitness of thinking and movement played a preponderating role in the preservation of the species.” It was the crucible of our evolution.

Unfortunately for Dart, other anthropologists were reluctant about admitting A. africanus to the human family, especially when so many fascinating discoveries were being made at Dragon Bone Hill in China, but he would ultimately be vindicated. His Taung child represented an early species of human – or hominin, in today’s jargon – after all, but the ecological milieu in which it lived was quite different from what Dart had presumed.

Contrary to the well-known pirate aphorism “Dead men tell no tales”, every fossil skeleton has multiple stories to tell. Fossilized bones contain clues as to the evolution of the species they represent, the life (and, often, death) of that individual, and the kind of environment in which that organism lived. This latter class of clue is subtle, but if you know where to look it is possible to begin to reconstruct what certain places were like in the distant past, and some hints about the habitat around Taung about 2.3 million years ago can be found among the remains of fossil baboons.

As reported by paleontologists Frank L’Engle Williams and James Patterson in the latest issue of the journal PALAIOS, the microscopic damage preserved on the second molar of fossil primates provides one way to peer into the ecological history of Taung. These pits and scratches were made by different kinds of plant food as the animals chewed some of their last meals. A baboon which primarily fed on grass would have many scratches on its teeth but few pits, one which subsisted on leaves would have few pits or scratches, and one which specialized in hard foods (such as seeds and nuts) would have many pits and scratches. By looking at all these trends together – as seen on part of the second molar called the paracone – the scientists hoped to gain an overview of what kinds of plants were present in the area, and this information, in turn, would provide hints as to what kind of ecologial setting the primates lived in. To do this, Williams and Patterson made second molar casts for the baboons Parapapio antiquus (8 specimens), Papio izodi (12 specimens), and 10 indeterminate specimens from Taung, and they compared the microwear seen on these teeth with tooth damage among baboons from a similarly-aged site at Sterkfontein (also in South Africa) and the extant Chacma baboon (Papio ursinus).

When the scientists compared the data taken from the different baboon molars, they found a disjunction between living and fossil species, and even relatively clear differences between fossil genera. Much like the living Chacma baboon, the fossil species Papio izodi appeared to have a flexible feeding strategy with a wider range and pit and scratch patterns, whereas the three Parapapio species (one from Taung and two from Sterkfontein) had wear patterns which fell more closely together, as did most of the indeterminate specimens. Despite some overlap, each species apparently had slightly different diets, yet none of the fossil species fell within the classic “browser, grazer, or hard-object specialist” triangle so often used in these kinds of studies. Taken as a whole, the fossil baboons showed a variable frequency of pits on their teeth – from few to many – but there was a general paucity of scratches. What kind of diet would produce pits, but few scratches?

As recognized by Williams and Patterson, Chacma baboons regularly eat corms, roots, and tubers – foods often placed under the larger heading of “underground storage organs.” Since they need to be dug out of the ground, these foods are often covered with grit which can cause pitting on teeth, but whereas Chacma baboons often brush or wash off this extraneous matter prior to consumption, the fossil baboons may not have done the same. If this were the case, Williams and Patterson hypothesize, it could explain the high number of pits and low number of scratches on the baboon teeth from Taung and Sterkfontein. The question is what kind of environment this pattern suggests. Underground storage organs are found in both dry environments and relatively more lush environments along rivers, and while the authors favor the latter setting for Taung, there is relatively little discussion of why their study supports this interpretation.

Interestingly, the cause of death of these baboons might provide stronger hints as to what Taung was like 2.3 million years ago. Many of the fossil monkey remains were not individuals who just happened to expire there, but had been brought there by predatory birds, as was the Taung child. These primates were victims of large raptors – much like many monkeys in tropical jungles today – and the bones of many primates and medium-sized mammals found at Taung show characteristic scratches created by the feeding habits of these birds. It is another startling case of predators creating part of the fossil record through their feeding habits (much like the giant hyenas which created the Dragon Bone Hill assemblage and the “horned” crocodile which fed on Homo habilis“horned” crocodile which fed on Homo habilis), and as L.R. Berger and R.J. Clarke hypothesized when they announced this discovery in 1995, it probably means that Taung was once a more forested habitat, with denser cover along waterways – a suitable habitat for a large bird with a taste for primates.

What this means for the habitat at Taung is that, even though the local ecology was still becoming drier and grasslands were expanding, at about 2.3 million years ago it was an open woodland – a forest in which there were many trees but little shade. It was not the dry, scrubby habitat which can be seen around Taung today, nor was it the open savanna seen in other parts of South Africa. The climate and ecology of South Africa was not as stable as had been presumed 100 years ago.

During Dart’s time, it was popular to create heroic origin stories about the early evolution of our lineage. Dart disagreed with other paleoanthropologists over where humans originated, but parties on both sides of the argument believed that an open, harsh habitat was required to drive our evolution – had our ancestors stayed in the forest, our lineage may never have reached its full potential. Some of these stories are considered in Misia Landau’s excellent study Narratives of Human Evolution, but we would be foolish to think that, at the beginning of the 21st century, we have given up spinning such yarns. On the contrary, where Dart used the hypothesis of environmental stability to bolster his argument for human evolution, rapid environmental change is now charged with keeping the tempo of human evolution, with popular-audience programs like the recent PBS series Becoming Human suggesting that we are adapted to change itself. There is a true story of human evolution – of the lives and deaths of humans which existed over the past six million years – but we are constantly tempted to give these stories a more dramatic veneer, a gloss which flatters our egos just enough for us to believe in an inevitable “rise from the ape.”

DART, R. (1925). Australopithecus africanus: The Man-Ape of South Africa Nature, 115 (2884), 195-199 DOI: 10.1038/115195a0

WILLIAMS, F., & PATTERSON, J. (2010). RECONSTRUCTING THE PALEOECOLOGY OF TAUNG, SOUTH AFRICA FROM LOW MAGNIFICATION OF DENTAL MICROWEAR FEATURES IN FOSSIL PRIMATES PALAIOS, 25 (7), 439-448 DOI: 10.2110/palo.2009.p09-116r

Berger, L. (1995). Eagle involvement in accumulation of the Taung child fauna Journal of Human Evolution, 29 (3), 275-299 DOI: 10.1006/jhev.1995.1060