EXCALIBOR - Empirical and experimental calibration of a clumped isotope (paleo)thermometer for bioapatites

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The abundance of 13C-18O bondings (clumped isotopes, measured as D47) in carbonates is a direct measure of carbonate crystallization temperature, independent of the isotopic composition of the parental fluid. Clumped isotope analysis of carbonates, therefore, has become a new tool to reconstruct past marine and terrestrial temperatures. Biogenic apatites usually contain <10% carbonate that can be analyzed for its clumped isotopic composition, too. It has been suggested very recently that the temperature dependence of isotopic clumping in bioapatites is sufficiently high to resolve from analysis of teeth whether dinosaurs were ecto- or endothermic organisms.We have successfully established the technique for clumped isotope analysis of carbonates and carbonate inside bioapatites. Our first results indicate that the temperature dependence of D47 of bioapatite might be less pronounced than previously assumed. We request funding to be able to complete our bioapatite T - D47 calibration for bioapatites and to study whether bioapatite composition and kinetics may affect D47 of CO2 resulting from phosphoric acid digestion of (bio)apatites. For this purpose, we will analyze D47 of enamel/enameloid and dentin from teeth of taxa with known body temperatures and from carbonate-bearing inorganically precipitated hydroxylapatites.Our results will be essential for evaluating whether D47 analyses of fossil bioapatites have the potential to deliver body temperatures of extinct vertebrates.