Palaeobiology of red and white blood cell-like structures, collagen and cholesterol in an ichthyosaur bone

Abstract

Carbonate concretions are known to contain well-preserved fossils and soft tissues. Recently, biomolecules (e.g. cholesterol) and molecular fossils (biomarkers) were also discovered in a 380 million-year-old concretion, revealing their importance in exceptional preservation of biosignatures. Here, we used a range of microanalytical techniques, biomarkers and compound specific isotope analyses to report the presence of red and white blood cell-like structures as well as platelet-like structures, collagen and cholesterol in an ichthyosaur bone encapsulated in a carbonate concretion from the Early Jurassic (~182.7 Ma). The red blood cell-like structures are four to five times smaller than those identified in modern organisms. Transmission electron microscopy (TEM) analysis revealed that the red blood cell-like structures are organic in composition. We propose that the small size of the blood cell-like structures results from an evolutionary adaptation to the prolonged low oxygen atmospheric levels prevailing during the 70 Ma when ichthyosaurs thrived. The δ13C of the ichthyosaur bone cholesterol indicates that it largely derives from a higher level in the food chain and is consistent with a fish and cephalopod diet. The combined findings above demonstrate that carbonate concretions create isolated environments that promote exceptional preservation of fragile tissues and biomolecules.

Fossilised Biomolecules and Biomarkers in Carbonate Concretions from Konservat-Lagerstätten

“…Carbonate concretions have been found to preserve the soft tissues of plants and animals throughout sedimentary rocks of all geological ages [54,55]. Carbonate concretions have been extensively studied [8][9][10]35,56], as they have the potential to contain an abundance of information regarding the conditions allowing for the exceptional preservation of fossils [57] ( Figure 1). The exceptional preservation of biological remains inside concretions is attributed to carbonate precipitation induced by microbial activity surrounding a decaying carcass or plant.…”

“…While these lipid biomarker studies provided evidence that highly sulfidic conditions contributed to the preservation of organic The exceptional preservation of biological remains inside concretions is attributed to carbonate precipitation induced by microbial activity surrounding a decaying carcass or plant. This microbially induced carbonate deposition, commencing immediately upon decay, prevents the full decomposition of the enclosed biological material for tens to hundreds of millions of years [8]. In nature, many microorganisms are known to induce carbonate precipitation by altering the solution chemistry through a wide range of physiological activities such as photosynthesis, ureolysis, ammonification, denitrification, sulfate reduction, anaerobic sulfide oxidation and methane oxidation [58].…”

“…In contrast, recent pioneering studies have shown that a much wider biological range of exceptionally preserved soft tissue, cellular remains and molecules are encapsulated inside the so-called carbonate concretions that are found in sediments of all geological ages [8][9][10]. Notably, the oldest-known intact lipids (cholesterol) were reported inside a 380-Ma-old Devonian concretion [10].…”

“…Notably, the oldest-known intact lipids (cholesterol) were reported inside a 380-Ma-old Devonian concretion [10]. Moreover, the detection of cholesterol, red and white blood cells and collagen in a 183-Ma-old fossil vertebra bone encapsulated in a carbonate concretion provided unprecedented insights into the predatory lifestyle and diet of an ichthyosaur-like reptile [8].…”

Hydrocarbon biomarkers preserved in carbonate veins of potentially Paleoproterozoic age, and implications for the early biosphere

“…A preferential preservation of biomarkers in the carbonate minerals of both vein types could further be possible, if the carbonate was porous at some stage. For instance, sterols and other intact biomarkers were found in Devonian and Jurassic carbonate concretions (Lengger, Melendez, Summons, & Grice, 2017;Melendez, Grice, & Schwark, 2013;Melendez, Grice, Trinajstic, et al, 2013;Plet et al, 2017). The mechanism of this protection in carbonate concretions may be similar to the protection of the biomarkers detected in the carbonate veins, in this study.…”