A novel ontogeny-related sampling of dental tissues for stable isotopes interpretation of the paleobiology of the cave bear

Abstract

In cave bear studies, stable isotope analysis of carbon and nitrogen is typically conducted on bone collagen. However, challenges arise due to biases in the classification of bones into age groups, which can be influenced by various factors that affect bone size. To overcome such issues, we present and evaluate a novel approach that involves sampling dental collagen from different ontogenetic stages of 45 fossil teeth, where only a portion of each tooth formed during the periods of interest was sampled. This approach enabled us to obtain a carbon and nitrogen fingerprint specific to a particular period in a cave bear’s life without interference from earlier stages. Stable isotopic analysis revealed a rapid decrease in δ15N values from 3 to 15 months of age. After that, the δ15N values remain stable. Based on the nitrogen isotope composition (15N/14N), cubs aged 0–3 months exclusively consumed milk, while the gradual introduction of solid plant food occurs at 5–10 months, resulting in a shift in δ15N values. Based on similar δ15N values in older age groups, it can be assumed that juveniles did not resume milk suckling after the first hibernation. The δ13C values increase until 15 months, followed by a gradual decrease until adulthood, potentially attributable to hibernation. The δ13C values also seems to indicate isotopic differences between yearlings with low δ13C values that successfully established hibernation and those with high δ13C values that failed to hibernate and starved. This novel observation, i.e., decreasing δ13C values from the second year of life onward, agrees with predicted isotopic skeletal collagen δ13C values calculated from modern brown bear blood plasma. In summary, the ontogenetic sampling strategy facilitated the acquisition of further paleobiological insights into the distinct life periods of cave bears.