The first direct evidence of what our earliest ancestors ate has been discovered due to a two million-year-old mishap that befell two early members of the human family tree.
The find has provided the most robust evidence to date of what at least one pair of hominins consumed. This remarkable research is published in the online edition of the prestigious journal Nature on Wednesday, 27 June 2012, and will appear in the 5th July print edition.
“The find is unprecedented in the human record outside of fossils just a few thousand years old. It is the first truly direct evidence of what our early ancestors put in their mouths and chewed – what they ate,” says Prof. Lee Berger, Reader in Human Evolution and the Public Understanding of Science at the Institute for Human Evolution at the University of the Witwatersrand, Johannesburg, who led the team comprising of nine leading scientists from across the globe. The lead author is Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Germany, a specialist in dental calculus and tartar.
Other specialists on the multidisciplinary team included dental micro-wear specialists, isotopic specialists and phytolith researchers – scientists whom study the physical remains of ancient plants. “We have been very lucky to bring together such a diverse group of talented individuals to conduct this study,” says Henry.
The story so far
Almost two million years ago, an elderly female and young male of the species Australopithecus sediba fell into a sinkhole, where their remains were quickly buried in sediment. As a result of this death, parts of the teeth were extremely well-preserved which has now enabled scientists to analyse the teeth in three different ways. In 2010, Berger and his colleagues described the remains of these creatures.
Berger also noticed what appeared to be stains on the teeth and realised they were probably dental plaque – tartar or calculus – mineralised material that forms on teeth. Three types of analysis Peter Ungar, Distinguished Professor of Anthropology at the University of Arkansas and the scientist responsible for conducting the dental micro-wear studies explains: “We have a very unusual type of preservation in this instance as the state of the teeth was pristine.”
This preservation enabled the researchers to analyse the teeth in three different ways. Dental micro-wear analyses of the tooth surfaces and high-resolution isotope studies of the tooth enamel were conducted on these remarkably well-preserved teeth. In addition, because the teeth had not been exposed to the elements since death, they also harboured areas of preserved tartar build-up around the edges of the teeth. In this plaque, the scientists found phytoliths, bodies of silica from plants eaten almost two million years ago by these early hominins.
“It is the first time that we have been able to look at these three elements in one or two specimens,” says Ungar. Using the isotope analysis, the dental micro-wear analysis and the phytolith analysis, the researchers closed in on the diet of these two individuals, and what they found differs from other early human ancestors from that period. The micro-wear on the teeth showed more pits and complexity than most other australopiths before it. Like the micro-wear, the isotopes also showed that the animals were consuming mostly parts of trees, shrubs or herbs rather than grasses. The phytoliths gave an even clearer picture of what the animals were consuming, including bark, leaves, sedges, grasses, fruit and palm.
Tests were conducted on the surrounding sediments to ensure the samples from the plaque were really part of the diet, and not contamination. “By testing the sediments in which the hominid was buried we can be sure that the phytoliths in the calculus were not from post depositional contamination,” says Prof. Marion Bamford from the Bernard Price Institute for Palaeontology at the University of the Witwatersrand, who worked on the phytolith analysis.
“I found the evidence for bark consumption the most surprising,” says Berger. “While primatologists have known for years that primates, including apes, eat bark as a fallback food in times of need, I really had not thought of it as a dietary item on the menu of an early human ancestor.” Matt Sponheimer, a Professor at the University of Colorado, Boulder, who worked on the isotopic research elaborates: “The results suggested a different diet than we have found in other early hominins, and were rather like what we find in living chimpanzees. We were not expecting Sediba to look unlike Australopithecus and Homo as various researchers have suggested affinities to one genus or the other, or both.”
Ungar adds: “These findings tell us a really nice story about these two individuals. We get a sense of an animal that looked like it was taking advantage of forest resources. This kind of food consumption differs from what has been seen in evidence from other australopiths. They come out looking like giraffes in terms of their tooth chemistry. A lot of the other creatures there were not eating such forest resources.”
“To think that we have direct evidence of what these near humans put in their mouths and chewed, still preserved in their mouths after two million years is pretty remarkable,” concludes Berger.