EXCEPTIONAL PRESERVATION IS NOT THAT EXCEPTIONAL: NEOPROTEROZOIC-TO-RECENT FOSSILS SHARE THE SAME MECHANISM OF BIOMOLECULE FOSSILIZATION

Carbonaceous fossils are known for all major groups of life and provide pivotal insights into the evolution of organismal form and function. Even though globally distributed throughout the Neoproterozoic and Phanerozoic, carbonaceous soft part preservation is considered exceptional based on the assumption that biomolecular building blocks have a low fossilization potential. Different taphonomic windows (e.g., BST preservation) linked to different sedimentological and ecological parameters are used to distinguish modes of preservation of carbonaceous fossils. However, patterns in the composition of carbonaceous fossils from different ages and settings are unknown, preventing a holistic understanding of mechanisms involved in exceptional preservation. Characterization of the total molecular composition of almost 300 Neoproteozoic-Recent carbonaceous fossils, associated sediments, and modern tissue analogues using high-resolution in situ Raman microspectroscopy allows to identify key fossilization reactions by means of multivariate statistics. The molecular composition of fossils is distinct from sedimentary organic matter and generally reflects N-, O-, S-heterocyclic polymers with different degrees of oxidative modification. In all cases fossilization involves oxidative crosslinking of original proteins, lipids, and sugars, regardless of the taphonomic window. Crosslinking follows either advanced lipoxidation or glycoxidation schemes depending on the original tissue composition: lipid- or sugar-derived reactive carbonyl species crosslink with adjacent nucleophilic amino acid residues of proteinaceous matter. Analyses of sediments identify dissolved or clay mineral-bound transition metals, depending on the depositional setting, as catalyzers of the synthesis of reactive carbonyl species. Early diagenetic crosslinking appears to be the key process allowing endogenous organic matter to survive in deepest time, and offers new perspectives for the preservation of biosignatures in all kinds of fossils.