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

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.