Sediba reveals what he ate

THESE hominins clearly didn’t brush their teeth on the morning nearly two million years ago that they fell into a sinkhole. Remains of their meal have been found in plaque in their teeth.

Microscopic image of small bulliform or grass leafThe 1.9-million-year-old Australopithecus sediba, found in the Cradle of Humankind in 2008 by professor Lee Berger of Wits University, reveal that these hominins ate parts of trees, shrubs or herbs. While examining the teeth of the two individuals so far excavated, Berger noticed stains or plaque on the teeth of tartar or calculus, a mineralised material that forms on teeth.

“In this plaque, the scientists found phytoliths, bodies of silica from plants eaten almost two million years ago by these early hominins,” the researchers say in a statement. The well-preserved teeth were analysed in different ways. Dental micro-wear analyses of the tooth surfaces and high-resolution isotope studies of the tooth enamel were conducted.

“We have a very unusual type of preservation in this instance as the state of the teeth was pristine,” says Peter Ungar, the distinguished professor of anthropology at the University of Arkansas and the scientist responsible for conducting the dental micro-wear studies of the teeth. The research was published in the online edition of the prestigious journal Nature yesterday, and will appear in the 5 July print edition.

The main 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 who 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.

Dental analysis
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. The phytoliths gave an even clearer picture of what the animals were consuming, including bark, leaves, sedges, grasses, fruit and palm,” indicates the statement.

Tests were conducted on the surrounding sediment in the area, to ensure the samples from the plaque were really part of the diet, and not contamination from elsewhere. “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 professor Marion Bamford from the Bernard Price Institute for Palaeontology at Wits University, who worked on the phytolith analysis.

“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,” adds Ungar. “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.”

Science
The research has created great excitement in the scientific world. “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 Berger, the reader in human evolution and the public understanding of science at the Institute for Human Evolution at Wits. He led the team of nine senior scientists from across the globe.

“I found the evidence for bark consumption the most surprising,” Berger adds. “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, explains: “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.”

New hominin species
In 2010, Berger and his colleagues unveiled the 2008 find, an entirely new hominin species. In September 2011, the almost complete hand skeleton of sediba was unveiled, together with the brain, hip, foot and ankle. Five papers detailing the findings and analysis of the discovery were published in the prestigious journal Science.

The very evolved hand has a long thumb, like a human, with long arms like an ape. This indicates that sediba was bipedal but was also able to climb. The hand also suggests that sediba was capable of tool manufacture and use. The advanced pelvis and long legs suggest it was able to stride and possibly even run like a human. Sediba has been described as a “transitional species” between Australopithecus africanus and either Homo habilis or Homo erectus.

Other animal fossils have been found with the sediba bones – sabre-toothed cats, hyenas, antelopes, mice, birds and snails. Sediba is a Sotho word for a well or a spring; the species was so named because it was hoped that “a great source of information will spring from the fossils”.