CALCIUM ISOTOPE FRACTIONATIONS IN VERTEBRATES FROM MODERN AND FOSSIL ECOSYSTEMS

Calcium isotope composition of vertebrate animal bioapatite is thought to be largely controlled by diet. Though a number of vertebrate samples have been analyzed for calcium isotope values, careful, systematic studies of terrestrial ecosystems are lacking. In order to better understand how trophic level and diagenesis potentially affect calcium isotope values in vertebrate tissues, we analyze samples from modern and Miocene fossil ecosystems that are well characterized in terms of other isotope systems (e.g., carbon). We pair large-bodied carnivorans and herbivorous mammals ranging from approximately 10 kg to >1000 kg from these study areas to examine trophic level effects. We also pair bone and tooth samples from individuals to assess potential diagenetic alteration. Samples were dissolved in HF and HNO₃. in preparation for analysis. A calcium double spike of known isotopic composition was added to each sample solution, which was then passed through an ion exchange resin column for purification and isolation of calcium. Each purified sample was analyzed in duplicate by thermal ionization mass spectrometry and corrected for instrumental mass fractionation by calculations using the double spike.

Initial results indicate that carnivores show consistently lower calcium isotope values when compared to herbivores, confirming intra-ecosystem trophic level effects. Though tooth and bone pairs show significant offsets in some cases, the magnitude of diagenetic effects is not immediately obvious. Calcium isotope values from bones and teeth may be providing slightly different information about an individual’s calcium physiology or the two tissues may be affected differently by other biological processes and/or timing of life history events.