METAZOAN BIOMOLECULE FOSSILIZATION PRODUCTS RECORD PHYLOGENY, PHYSIOLOGY, AND BIOMINERALIZATION

Proteins, lipids and sugars are the key building blocks of all animal life. These molecules contain biological information of different kinds: their relative abundance identifies tissue types, abundant chelates reveal biomineralization, oxidative plaques record metabolic rates, and the protein sequence stores phylogenetic information. Diagenetically altered biomolecular remnants have been documented in many fossils but patterns and processes in the fossilization of animal proteins, lipids, and sugars are poorly known, and the potential for preserving biological signals in fossil biomolecules remains largely unexplored. We characterized the molecular composition of a sample of more than 100 Phanerozoic metazoan fossils and their associated sedimentary matrix using high-resolution in situ Raman microspectroscopy and analyzed the data. The chemistry of soft tissues in metazoan fossils is distinct from that of the surrounding sedimentary organic matter. The composition of originally distinct biomolecules converges structurally through oxidative crosslinking of amino acid residues (proteins) with either lipid- or sugar-derived reactive carbonyl species to form N-, O-, and S-heterocyclic polymers. Nonetheless multivariate spectral analysis reveals characteristic molecular heterogeneities in these crosslinked products which preserve biological signals. Lipid- and sugar-based protein crosslinks retain differences diagnostic of particular tissue types. Preserved chelating ligands are characteristic of original protein-mineral interactions reflecting biomineralization. Comparable vascular tissues retain baseline signals of oxidative plaques formed in vivo indicating metabolic rates. In non-vascular tissues, distinct crosslinked products preserve the ratio of amino acids in proteins providing evidence of higher-rank metazoan relationships. Thus fossil biomolecules represent a novel and powerful tool for assessing evolutionary history.