Is the presence of biomolecules evidence for molecular preservation in the fossil record?

The molecular components of life (i.e., biomolecules such as DNA, proteins, lipids) have the potential to preserve in animals that have been extinct for millions of years, offering a scale of analysis previously inaccessible from the fossil record. As new technology (e.g., high resolution mass spectrometry) has been incorporated into fossil analyses, researchers have begun to detect biomolecules in terrestrial vertebrates dating back to the Triassic Period (~230 Ma). However, these biomolecules have not been demonstrated to be the biological remains of these ancient animals and may instead be exogenous organic contaminants. Here, I developed a series of analytical techniques to detect and interpret the preservation of the degraded remains of the most common protein in bone, collagen, in terrestrial vertebrates from two time slices that represent the two ends of the preservation spectrum: a "shallow time" study of fossils <150,000 years old from different burial environments (i.e., permafrost, fluvial and hot springs) and a deep time study of dinosaurs (~212 - 66 Ma) from the same burial environment (i.e., fluvial), representing the current limit of the reported protein preservation in the fossil record. Unlike previous studies that have focused on organic extractions to detect biomolecules, I studied intact fossil bones and the rocks they were found in, to understand more about the effect of burial conditions on preservation and potential alternative sources of organic compounds. I found endogenous amino acids (the degradation products of proteins) and lipids in the mammoth bones, although they were already heavily degraded in fluvial environments, even on such short timescales. I also found that there were amino acids and lipids preserved in the dinosaur bones, however tests on the age of the amino acids and the types of lipids present, demonstrate that they are not original to the animals in this study. Therefore, fluvial environments, one of the most common depositional environments preserved in the geologic record, are not conducive to the preservation of proteins on long timescales and researchers should be cautious when using these biomolecules to make interpretations about the biology of ancient animals.