Evidence for herbivorous cave bears (Ursus spelaeus) in Goyet Cave, Belgium: implications for palaeodietary reconstruction of fossil bears using amino acid 15N approaches

Insights into causes of extinction in fossil animals can contribute to an understanding of how environmental or anthropogenic processes may affect extant animals. Cave bears that went extinct in the late Pleistocene in Europe have been considered largely herbivorous based on tooth, skull and jaw morphology. Nitrogen and carbon isotopic composition (N-15, C-13) of bone collagen of many cave bears having values similar to or lower than those of coeval herbivores support an exclusive plant diet and their occurrence in habitats with denser vegetation. A complicating aspect of this hypothesis is that isotopic compositions of bulk collagen, especially those of nitrogen, could reflect environmental fluctuation as well as behavioural and physiological traits, which are not related to trophic position and so may lead to uncertainty in palaeodietary reconstruction. Here we show that N-15 analysis of individual collagen amino acids of fossil bears from Goyet Cave (Belgium) indicates that cave bears had a constant trophic position of 1.9-2.1, indicating purely herbivorous diets, while brown bears had a trophic position of 2.0-2.4, indicating a slightly more omnivorous diet. Results might support the hypothesis of the extinction of cave bear due to the inflexibility in feeding habits.