Ancient dental plaque sheds light on Easter Islanders' diets

December 17, 2014

Image Credit: Thinkstock

John Hopton for redOrbit.com Your Universe Online

Those working in the field of history will often point out that it is not as glamorous as the Indiana Jones movies make it, and for a PhD student digging the remnants of ancient food from teeth excavated on Easter Island, that is certainly the case. Indiana Jones and the Hardened Plaque does not have the ring of a box office smash, but hardened plaque, also known as dental calculus, is helping us to understand the diets of the fascinating ancient culture that gave us the world famous stone heads.

The study concerns whether or not palm was part of the diet of natives of Easter Island, known locally as Rapa Nui. Biological anthropologists Monica Tromp, a University of Otago, New Zealand, PhD student, and Idaho State Universitys Dr. John Dudgeon conducted a previous study which suggested that palm was part of Easter Islanders diets. But this was confusing because no other archaeological or ethnohistoric evidence supports palm having a dietary role on Rapa Nui. Rather, evidence suggests that palm became extinct soon after colonization in the thirteenth century.

The latest study points to the traces of palm in the calculus being from the environment that food was grown in, rather than from the food itself. Such a finding will impact the study of dental calculus worldwide.

Thirty teeth from burials excavated in the early 1980s were analysed, and the results were published in the Journal of Archaeological Science. This included identifying starch grains in the dental calculus after removing and decalcifying the plaque from each tooth. Ms Tromp and Dr Dudgeon identified starch grains that were consistent with modern sweet potato, while none of the grains showed any similarities to banana, taro or yam, or other starchy plants that are posited to be part of the diet.

The researchers then tested modern sweet potato skins grown in sediment similar to that of Rapa Nuis and found that as tubers grow, their skins appear to incorporate palm phytoliths from the soil. They found that the vast majority of phytoliths (plant microfossils) embedded within the calculus were from palm trees.

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, says Ms Tromp. She adds that plaque is an excellent target for looking at the plant component of ancient diets as microfossils become embedded in dental calculus throughout a persons life. You can get a good idea of some of the plant foods people were eating, which is not an easy task. It is particularly difficult when assessing the role of plants in Oceanic diets because of the scarcity of plant remains.

On a related note, it was reported in October that the use of sweet potatoes on Rapa Nui is evidence of ancient interaction between people from the isolated Pacific island and natives of South America. It is thought that Easter Islanders may have sailed to South America some time between 1300 and 1500, long before Europeans arrived.

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Ancient dental plaque sheds light on Easter Islanders' diets