Pterosaur and Ichthyosaur Fossils Reveal Microbial Role in Three-Dimensional Preservation

Both investigations highlight the role of microorganisms and specific mineral formation in preserving ancient biological material.

Pterosaur Wing Bone: Preservation and Molecular Analysis

A pterosaur wing bone fossil, approximately 100 million years old, was discovered in the Romualdo Formation in northeastern Brazil. The fossil was preserved inside a carbonate concretion.

High-resolution CT scanning and mineral analysis revealed microscopic inner structures and molecular traces. Microbes facilitated decay but also triggered the rapid formation of phosphate minerals, including fluorapatite, which stabilized delicate features. Barite and celestite—minerals associated with sulfur-using bacteria—were detected, indicating microbial activity contributed to the preservation process. Subsequent calcite layers formed from carbon released during fatty tissue decay, acting as a geological vault protecting organic compounds.

The fossil contained steranes, steroid biomarkers derived from lipids, reported for the first time in a pterosaur fossil. Carbon isotope analysis of cholesterol-derived compounds suggested the pterosaur fed on fish or squid-like marine animals. Microscopic structures resembling collagen fibers were preserved, with patterns similar to those in modern birds.

"The research demonstrates that molecular traces of life can survive for over 100 million years under appropriate conditions."

The methods used may help identify other fossils capable of preserving ancient biomolecules, potentially including DNA fragments.

Ichthyosaur Fossil: Mechanism for Three-Dimensional Preservation

Scientists at Curtin University, in collaboration with Kiel University, conducted research detailed in Communications Earth & Environment on a 183-million-year-old ichthyosaur, a marine reptile, discovered preserved within a carbonate concretion in Germany's Posidonia Shale.

After the ichthyosaur's death, its remains settled on the anoxic seafloor. Anaerobic sulfur-cycling microbes colonized the decaying tissues. As these microbes processed the fatty tissues, they initiated chemical reactions that resulted in the formation of various minerals within the bones. The mineral barite developed deep within the bones, indicating the presence of localized oxidizing conditions. Concurrently, calcium carbonate formed around the bones, creating a protective hard rock shell. This process fortified the skeleton, preventing its collapse under the weight of accumulating sediment.

Previous scientific understanding suggested that the absence of oxygen on the seafloor was the primary factor in slowing decay and preserving such fossils. However, observations of oxidation within these fossils from anoxic settings presented a long-standing paradox. According to lead author Andrew Jian, the microbes effectively reinforced the bones with minerals. Senior author Professor Kliti Grice stated that these findings significantly alter the understanding of fossil preservation, highlighting that the sulfur cycling microbiome and internal chemical processes play a critical role, even in oxygen-deficient settings.

"This research may also contribute to a better understanding of life in Earth's past extreme environments and could inform the search for signs of life on other planets."

The study, titled ‘Microbial oxidation and carbonate cementation led to 3D preservation of ichthyosaur bones’, was supported by the Australian Research Council.