Assessing the Utility of Strontium Isotopes in Fossil Dental Calculus

Strontium (Sr) isotopes measured in fossil remains have been a useful tool to assess the geographical origin and even migrations of humans and other animals. In particular, dental enamel generally represents the ideal material, as it is dense and less prone to diagenetic replacement of Sr post-burial. However, fossil teeth can often be precious artefacts and difficult to access for destructive analysis. Here, we assess whether measuring Sr isotopes in fossil dental calculus could be used at least as a rangefinder to determine the geographical origin of an individual. We measured trace element concentrations in modern calculus (from a local dental practice), and trace element concentrations and ⁸⁷Sr/⁸⁶Sr ratios in human fossil calculus, dentine, and enamel from specimens collected in York, UK. Comparing trace element concentrations between modern and fossil calculus show that metals present in fossil calculus are mostly acquired post-burial, including Sr. The relationship between ⁸⁷Sr/⁸⁶Sr and Rb/Sr ratios in fossil calculus, dentine, and enamel suggests that the diagenetic end member would have a ⁸⁷Sr/⁸⁶Sr ratio consistent with the one modelled for the York region, but a low Rb/Sr. Without calculus data, dentine and enamel data would have probably suggested a lower ⁸⁷Sr/⁸⁶Sr ratio for a diagenetic end member, expecting high Rb/Sr values. Thus, while Sr isotopes in fossil calculus may not be useful to identify the geographical origin of an individual, they may be useful in constraining the composition of the diagenetic end member. Combining Sr isotopes in fossil dental calculus and enamel could be a more robust approach to identify geographical origin than using enamel alone.