Australasian Science: Australia's authority on science since 1938

Dental Plaque Reveals Easter Island Diet

Analysis of dental calculus from ancient teeth is helping to resolve which plant foods Easter Islanders relied on before European contact.

Known to its Polynesian inhabitants as Rapa Nui, Easter Island is thought to have been colonised around the 13th century and is famed for its mysterious large stone statues.

Otago University PhD student Monica Tromp and Dr John Dudgeon of Idaho State University have previously found that palm may have been a staple plant food for the population over several centuries. However, no other line of archaeological or historical evidence supports a dietary role for palm on Easter Island, with evidence even indicating that palm became extinct soon after colonisation.

Nevertheless, the researchers had found that the vast majority of plant microfossils (phytoliths) embedded within the calculus of burials at a number of archaeological sites were from palm trees.

Now further analysis published in the Journal of Archaeological Science has identified starch grains in the dental calculus removed from 30 teeth. The starch grains are consistent with modern sweet potato. None of the recovered grains showed any similarities to banana, taro or yam – other starchy plants that were thought to be part of the diet.

The researchers tested modern sweet potato skins and found that as tubers grow, their skins seem to incorporate palm phytoliths from the soil. “So this actually bolsters the case for sweet potato as a staple and important plant food source for the Islanders from the time the island was first colonised,” Tromp says.

Dental calculus “is an excellent target for looking at the plant component of ancient diets as microfossils become embedded in dental calculus throughout a person’s life,” she says. “This research also shows that the plant foods you find evidence for in dental calculus can come from the environment that foods are grown in and not necessarily from the food itself. This finding has the potential to impact dental calculus studies worldwide.”