Plaque found on two million-year-old teeth

A deadly mistake made two million years ago by two of humankind’s earliest ancestors has provided the first evidence of what food they ate – from an analysis of the plaque on their teeth.

“The find is unprecedented in the human record outside of fossils just a few thousand years old,” says Professor Lee Berger of the Institute for Human Evolution at the University of the Witwatersrand in Johannesburg. “It is the first truly direct evidence of what our early ancestors put in their mouths and chewed – what they ate.”

Berger led a team comprising nine top scientists from across the globe.

Lead author is Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Germany, a specialist in dental calculus and tartar, while other specialists included dental micro-wear specialists, isotopic specialists and phytolith researchers – scientists who study the physical remains of ancient plants.

The story begins almost two million years ago when an elderly female and a young male of the species Australopithecus sediba fell into a sinkhole where their remains were quickly buried in sediment. As a result, parts of their teeth were extremely well preserved and this enabled the scientists to analyse the teeth and what was on them.

Berger and his colleagues had earlier described the remains of the creatures and noticed what appeared to be stains on the teeth. They realised these were probably dental plaque – tartar or calculus – mineralised material that forms on teeth.

The 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.

Also, because the teeth had not been exposed to the elements, they harboured areas of preserved tartar build-up around their edges, and in the plaque the scientists found phytoliths – bodies of silica from plants eaten by the early hominins.

Using the isotope analysis, the dental micro-wear analysis and the phytolith analysis, the researchers were able to identify the diet and found it differed from other early human ancestors of the time.

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 the creatures were consuming mostly parts of trees, shrubs or herbs, rather than grasses.

“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.

“To think that we have direct evidence of what these near humans put in their mouths and chewed, still preserved after two million years, is pretty remarkable.”

The research is published this month in the online edition of Nature.