Testing the validity of stable isotope analyses of dental calculus as a proxy in paleodietary studies

Authors: Samantha D.R. Price, Anne Keenleyside, and Henry P. Schwarcz

Journal of Archaeological Science, Vol. 91, March 2018, pp. 92-103. DOI: https://doi.org/10.1016/j.jas.2018.01.008

Abstract

Stable isotopic analyses (δ¹³C, δ¹⁵N) of dental calculus have been suggested as a proxy for the study of diet of ancient populations but questions about their validity have been raised. Here we test this question, introducing significant improvements in the analysis of δ¹³C and comparing our results for δ¹³C and δ¹⁵N of calculus with corresponding analyses of associated well-preserved bone which are widely believed to provide reliable paleodiet values. The content of organic material in calculus is decreased by ∼75% compared with modern calculus, resulting in diagenetic changes to δ¹³C and δ¹⁵N of organic matter. Neither δ¹³C nor δ¹⁵N analyses of the organic component of calculus provide accurate estimates of paleodiet. Although δ¹⁵N values of dental calculus are correlated with δ¹⁵N values of bone collagen from the same individual, it is clear that they have been greatly affected by diagenesis, as shown by a correlation between C/N ratio and δ¹⁵N. The inorganic (mineral-bound) carbon component of calculus, analyzed separately from the organic component, gave δ¹³C values slightly offset from δ¹³C values of CO₃ in bone mineral. Thus it alone appears to have potential as a dietary proxy.

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