Metal Isotopes in Mammalian Tissues

Ecologists rely on a wealth of data, including field observations and light stable isotopes, to infer dietary preferences and other ecological and physiological properties in living mammals. But inferring such important traits (e.g., trophic position, metabolism, pathologies) in extinct animals, including humans, can be challenging because biological processes rarely mirror morphology as preserved in the fossil record. For instance, dietary behavior does not necessarily reflect tooth morphology. As an additional challenge, some isotopic mammal tissues commonly used in modern ecology, such as collagen in bone or dentin or keratin from hair, hoof, or horn, do not generally preserve in fossil remains older than ∼200 kyr. In contrast, major constituents of bioapatite often retain their initial isotopic composition through fossilization processes. Recent analytical developments in mass spectrometry now allow, using small samples, for assessment of isotopic variability of major and trace elements such as calcium or zinc. Here, we review the application potentials of metal (nontraditional isotopes) for (paleo)ecological, (paleo)physiological, and (paleo)mobility inferences as applied to mammalian research. ▪ Mammals are key elements of modern ecosystems and possess a rich evolutionary history, yet inferences about their past ecologies and physiologies are challenging to retrieve using traditional geochemical toolkits. ▪ Metal stable isotopes provide a novel and complementary approach to unveil paleoecological and paleophysiological characteristics of extinct mammal species. ▪ Within a 20-year time frame, the core of metal isotopic data in mammalian research remains small compared to traditional isotopic systems (C, O, N), which is inviting for designing cost-effective instrumentation and increasing dissemination across scientific disciplines.