A new non-destructive method to decipher the origin of organic matter in fossils using Raman spectroscopy.

Ancient biomolecules provide a unique perspective on the past but are underutilized in paleontology because of challenges in interpreting the chemistry of fossils. Most organically preserved soft tissues in fossils have been altered by thermal maturation during the fossilization process, obscuring original chemistry. Here, we use a comprehensive program of thermal maturation experiments on soft tissues from diverse extant organisms to systematically test whether thermally altered biosignatures can be discriminated using Raman spectroscopy. All experimentally matured samples show chemical signatures that are superficially similar. Comparative analysis of Raman spectra following peak deconvolution, however, reveals strong tissue-specific signals. Application of this approach to fossils from the Bolca (49 Ma) and Libros (10 Ma) Konservat-Lagerstätten successfully discriminates fossil vertebrate soft tissue from that of fossil plants. Critically, our data confirm that a robust interrogation of Raman spectra coupled with multivariate analysis is a powerful tool to shed light on the taxonomic origins of thermally matured fossil soft tissues.