Scientists have been pondering why people who lived on Easter Island (or Rapa Nui) appear to have eaten palm trees—a primary crop, reports Nature World News—for several centuries when other research suggests the plant went extinct right around the time of colonization in the 13th century.

The answer may have just been found in tooth plaque. It turns out that the 30 teeth scientists analyzed, which were taken from excavations at several coastal sites in the early 1980s, had plaque with starch grains that line up well with the modern sweet potato, reports Phys.org.

By studying actual modern sweet potatoes grown in soil similar to Rapa Nui's, they also found that the tuber skins took on palm phytoliths from the soil, explaining why original analyses suggested palm was part of the diet.

This marks the first time biological anthropologists have studied dental calculus in the Pacific, and they say it makes a case for taking into consideration the environments the plants were grown in and not just the plants themselves.

(Meanwhile, genetic data suggests Easter Islanders were not as isolated as once thought.)

This article originally appeared on Newser: Teeth Solve an Easter Island Mystery

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