Dentin collagen sample geometry impacts pattern of intra-tooth nitrogen and carbon isotope change in taurine teeth

Sequential stable isotope analyses of hypsodont ruminant molars provide insights into animal behavior and human-animal interactions at seasonal scales. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios obtained from intra-tooth sequences of dentinal collagen inform on animal weaning and feeding habits, but sequential sampling of this tissue is rarely carried out in part due to the undefined relationship between dentin geometry, sample position, and measured isotope values. Here, we present a serial sampling approach applied to dentin collagen from modern and archaeological taurine second molars that entails sub-sampling the outermost portion of the dentin structure. Compared to intra-tooth isotope sequences measured from the entire thickness of the dentin structure, nitrogen isotope sequences obtained from the outermost dentin portion better capture the weaning process, while carbon isotope values reveal subtle but discernible shifts in C₃ dietary intake that were not visible in dentin portions involving the entire dentin thickness. The ability to document dietary change at higher resolution has important implications for gaining more nuanced insights into livestock husbandry practices in the past, including foddering, weaning, and pasturing.