Ancient biomolecules: Their origins, fossilization, and role in revealing the history of life

Abstract

The discovery of traces of a blood meal in the abdomen of a 50-million-year-old mosquito reminds us of the insights that the chemistry of fossils can provide. Ancient DNA is the best known fossil molecule. It is less well known that new fossil targets and a growing database of ancient gene sequences are paralleled by discoveries on other classes of organic molecules. New analytical tools, such as the synchrotron, reveal traces of the original composition of arthropod cuticles that are more than 400 my old. Pigments such as melanin are readily fossilized, surviving virtually unaltered for ∼200 my. Other biomarkers provide evidence of microbial processes in ancient sediments, and have been used to reveal the presence of demosponges, for example, more than 635 mya, long before their spicules appear in the fossil record. Ancient biomolecules are a powerful complement to fossil remains in revealing the history of life.

Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

“…[65] In some cases, biomolecules may remain as biomarkers in the rock when all morphology is lost. [10] Bond strengths, functional groups, and steric effects influence the susceptibility of different biomolecules to degradation. [9] Nucleic acids are the least stable, followed by proteins, carbohydrates, lipids, pigments, and structural macromolecules.…”

“…[9] Nucleic acids are the least stable, followed by proteins, carbohydrates, lipids, pigments, and structural macromolecules. [9,10] Under certain conditions, it is possible to recover more resistant biomolecules associated with fossils in a nearly intact state. Recently, for example, sterols have been reported in a 380 million-year-old Devonian crustacean preserved in a concretion [66] and nearly intact melanin in a 200 million-year-old coleoid cephalopod.…”

“…[8] Despite the diversity of settings that yield exceptionally preserved fossils, many Konservat-Lagerstaẗten share biological and geological processes such as rapid burial, limited or no bioturbation, decay suppression through anoxia or euxinia, and sealing of sedimentary laminae by microbial mats and early diagenetic cements (Figure 1). These factors contribute to the survival of organic macromolecules [9,10] and create the necessary microenvironments for the replication of soft tissues through authigenesis, the early precipitation of minerals. [11] Understanding preservation (the field of taphonomy) is critical to interpreting the morphology of fossils and, in turn, their place in the tree of life and consequent significance for organismal evolution.…”

Sterol and genomic analyses validate the sponge biomarker hypothesis

“…The basic sterol of animals-cholesterol-consists of 27 carbons (or C 27 ), but modifications to the nucleus and/or side chain allow for a diversity of structures, typically ranging from C 26 -C 31 . Some of the most exotic sterols are restricted to particular eukaryotic lineages, and because sterols (diagenetically altered into steranes) are stable through deep geological time, they can function as "molecular fossils," recording the evolution of organisms even in the absence of physically preserved fossils (3).…”

Hopanoids as functional analogues of cholesterol in bacterial membranes

“…Hopanoids are some of the most ubiquitous cyclic isoprenoidal lipids in the sedimentary record, and they have been used as molecular proxies for ancient microbial life (5). Importantly, hopanoid synthesis does not require molecular oxygen, and hopanoids have been reported in sediments predating the enrichment of oxygen in Earth's atmosphere (6,7). Their discovery led to the proposal that they might serve as sterol surrogates in bacteria (8), especially because hopanoids and sterols share common structural features and are cyclized by closely related enzymes (9,10).…”