Isotopic uniformity and segregation in Tongan mounds

Oral traditions, historical sources and geochemical results indicate that Polynesian chiefly societies had extensive inter-island interactions. Tonga was often a central hub of these interactions, particularly during the Tongan state era (750-150 BP). Archaeological evidence for human migration and inter-island mobility based on isotopic data from human remains, however, is sparse. We used strontium isotope analysis of human enamel excavated from a burial mound in the elite chiefly precinct of Lapaha to investigate whether the remains of chiefly spouse exchanges known from oral tradition are present in the mound. Strontium ratios from the burial mound in the high-status area are compared to ratios measured in human enamel from three simple mounds likely to be the burial sites of non-elites and also to faunal samples and geological ratios. The analysis was supplemented by carbon and oxygen isotope analysis of enamel and carbon and nitrogen isotope analysis of bone collagen from selected human remains. Indications of laboratory error during analysis of one set of strontium samples led us to perform an inter-laboratory comparison of strontium analyses, with the results indicating that labs typically have error ranges that are about twice that reported as instrument error. Our results indicate that at most one individual has an isotopic signature suggestive of being an immigrant to the area. We also show that there is remarkable isotopic uniformity within and diversity among Tongan mounds, a pattern not previously encountered which suggests significant burial segregation among Tongan social groups or villages.