UnexpectedDinoLesson / Wikimedia Commons, CC BYMore than 100 million years ago, a flying reptile called a pterosaur flew over the oceans hunting squid and fish. Much more recently, one of its wing bones was discovered in Brazil, transformed over the aeons into a fossil made of a complex assemblage of different chemicals and minerals.And in new research published in iScience, my colleagues and I found that the fossil bone still holds secrets of the creature’s life, including microscopic inner structures of its bones and molecular traces of its biology and diet.A fossil treasure from BrazilThe fossil comes from the Romualdo Formation in the Araripe Basin of northeastern Brazil, one of the world’s most spectacular fossil deposits. The site has yielded exquisitely preserved fish, turtles, crocodile relatives, and pterosaurs.Many fossils from the Romualdo Formation are preserved inside rounded rock nodules known as carbonate concretions. These mineral structures form shortly after burial, effectively sealing the remains from the environment. Think of them as natural time capsules. A microscope view of a section of the pterosaur fossil shows its dark carbon coating and mineral layers. Grice et al. Our fossil is a hollow wing bone, or phalanx. Pterosaur bones were thin and lightweight to aid flight, so they are rarely preserved in such detail. Using high-resolution CT scanning, we examined the bone’s interior without breaking it open. The scans revealed layers of minerals with different densities filling the cavity – evidence of a complex sequence of chemical events that preserved the bone. We used several other methods to identify the minerals.Microbes helped decay – and preservationThe fossil’s exceptional preservation may have begun with decay. As the pterosaur’s body decomposed on the ancient seafloor, microbes broke down tissues and altered sediment chemistry. You had this reference as Jian et al. 2026 - I have added this link but please check it’s the right paper. ML These changes triggered the rapid formation of phosphate minerals.One mineral in particular, called fluorapatite, formed within and around the bone, stabilising delicate features before they could be lost. Under the microscope, we could still see microscopic canals that once carried nutrients through living tissue.Mineral analysis revealed evidence of microbial activity. We detected barite and celestite, minerals associated with sulphur-using bacteria. These microbes drove chemical reactions that helped create the conditions necessary for preservation.In other words, ancient microbes didn’t just decay the body, they also helped preserve it for science.A mineral vault for ancient moleculesAfter early phosphate minerals stabilised the bone, a sequence of calcite layers gradually formed inside and around it. These derived largely from carbon released during the decay of fatty tissue.First, a thin layer of fine-grained calcite formed along the bone surface, followed by a second, slightly coarser-grained one. Over a longer period of time, larger calcite crystals formed, ultimately filling the bone cavity. Analysis showed this calcite was low in an isotope called carbon-13, which indicates it partly came from organic carbon sources, such as fatty lipids and residual bone material. In contrast, any remaining organic matter in the bone appears to have relatively high levels of carbon-13.The multi-layered mineral barrier acted like a geological vault, protecting delicate structures and organic compounds trapped in the bone from chemical degradation for millions of years. This protection allowed molecular traces such as steroid biomarkers and collagen fibre patterns to survive, giving us a rare window into the biology and diet of this ancient flying reptile. Molecular traces of ancient lifeWithin this mineralised structure, we detected molecular traces of life called steranes, which are derived from steroidal lipids once present in living cells. To our knowledge, this is the first time steroid biomarkers have been reported from a pterosaur fossil.Even more exciting, these molecules carry dietary clues. Carbon isotope analysis of cholesterol-derived compounds suggests this pterosaur likely fed on fish or squid-like marine animals, which is what we would expect from the shape of its teeth and skull. The fossil also preserves microscopic structures resembling collagen fibres, the protein framework that strengthens bone. Although chemically altered over millions of years, the fibre patterns remain visible and resemble those seen in modern birds, which are distant relatives of pterosaurs. Reading fossils in new waysDiscoveries like this one are transforming how we study fossils. Instead of examining only bone shapes, we can now recover chemical and molecular fingerprints as well.Understanding how these exceptional fossils form may help identify other specimens capable of preserving ancient biomolecules. More broadly, our findings show that under the right conditions, molecular traces of life can survive for more than 100 million years.Even after millions upon millions of years, ancient life can still leave behind chemical clues waiting to be discovered. As analytical techniques continue to advance and unusual modes of preservation become better understood, there is increasing potential to recover previously inaccessible information. In the future, we may even be able to detect ancient DNA fragments or other molecular remnants in exceptionally preserved fossils, including those of dinosaurs and pterosaurs.Kliti Grice receives funding from the Australian Research Council. The specimen used in this research was provided by Associate Professor Renan A.M. Bantim and Professor Antônio A.F. Saraiva at the Regional University of Cariri, and Professor Alexander W.A. Kellner at the Department of Geology and Paleontology, Museu Nacional and the Federal University of Rio de Janeiro, UFRJ – who also contributed to this research and related projects.