Near-Atomic-Scale Characterization of Diagenetic Signatures in a Fossil Dinosaur Tooth by Atom Probe Tomography

Understanding the diagenesis of fossil teeth requires linking microstructure to chemistry across spatial scales to distinguish primary biogenic signals from diagenetic signals introduced by fluid-mineral interactions. Here, we investigate a Cretaceous theropod tooth using a multiscale analytical workflow that combines scanning and transmission electron microscopy with atom probe tomography. The results reveal a hierarchical pattern of diagenetic alteration in both enamel and dentine spanning from the microscale to the near-atomic scale. Enamel largely preserves its densely packed apatite crystallites yet contains sparsely distributed nanoscale precipitates enriched with secondary elements, indicating localized diagenetic modification. In contrast, dentine shows extensive diagenetic alteration, characterized by the infilling of dentinal tubules with secondary elements. Furthermore, both tissues exhibit intergranular segregation of C and Sr along apatite grain boundaries, a feature that has not been previously discussed in fossil dinosaur teeth. These observations demonstrate that diagenetic effects can extend down to the nanoscale, implying that bulk geochemical measurements with limited spatial resolution may integrate both preserved and altered domains. Our findings highlight the potential of atom probe tomography to advance the understanding of diagenesis and the biomineralization process.