The bacteria that began consuming a pterosaur's body 113 million years ago in an ancient Brazilian sea didn't destroy it. Through a chain of chemical reactions, they preserved it, sealing molecules inside the bone that have survived to be read today.
A new study published in iScience has recovered steroids from that fossilized wing bone, the first time any molecules have ever been extracted from a pterosaur fossil. The chemical signature of those steroids points to a diet of fish and squid, providing the first molecular evidence of what these ancient flying reptiles ate. It also points to oxygen, considered an enemy of fossil preservation, can, under the right conditions, do the opposite.
“This fossil is a true time capsule — not only is it beautifully preserved, but for the first time we’ve detected traces of steroids in a pterosaur, providing further evidence that these creatures likely fed on fish or squid,” said lead author Kliti Grice in a press release.
Read More: A 233-Million-Year-Old Fossil Reveals How Pterosaurs Learned to Fly
Pterosaur Fossil Molecules Reveal a Diet of Fish and Squid
Pterosaur fossil section showing carbon coating and mineral layers.
(Image Credit: Grice et al., iScience (2026))
The fossil is a wing phalanx, a single bone from the leading edge of a pterosaur wing, found in the Romualdo Formation of northeastern Brazil. The specimen belongs to a group called anhanguerids, large-bodied pterosaurs with wingspans that could reach up to 39 feet (12 meters) in some species.
Pterosaurs were the first vertebrates to achieve powered flight, living alongside dinosaurs until both groups went extinct at the end of the Cretaceous. Like modern birds, they had hollow bones, which, under the right conditions, increase the chances of good preservation.
The bone was preserved in three dimensions inside a rocky nodule that formed around it as it fossilized, with its internal structure, including individual bone cells and tiny nutrient channels, still visible.
The research team used advanced imaging and chemical analysis to look inside the bone at a molecular level. What they found were steroids, including cholesterol, whose carbon signatures reflect what the animal was eating and where it sat in the food chain.
How Bacteria and Oxygen Preserved the Fossil
When the pterosaur sank, the decay of its body produced acids that triggered an early wave of mineralization, coating and stabilizing the bone tissues before they could be lost. Sulfur-processing bacteria then created chemical conditions that drove three further rounds of mineral encrustation, progressively locking the organic compounds inside layers of stone.
“After this pterosaur died and sank to the seabed, a perfect storm of chemistry, biology and the environment worked to seal its story in stone,” said Grice.
What surprised the team was the role oxygen played. Normally considered destructive to organic material in fossils, localized pockets of oxygen around the decaying carcass appear to have actually driven the mineralization that preserved it.
“Steroid preservation in fossils is exceptionally rare, but what’s even more fascinating is that our findings challenge long-held ideas about fossil preservation itself,” said Grice. “Rather than being destroyed by oxygen, some fossils are preserved because of it, through oxidative processes carried out by ancient microbiomes.”
What Ancient Molecules Could Reveal About Pterosaurs
What happened to this pterosaur may not be unique. The Romualdo Formation is already known for its well-preserved vertebrates, and the team believes the same sequence of chemical events could be responsible for remarkable fossil preservation at other sites around the world.
Molecules from fossils can reveal diet, physiology, and ecology in ways that bone structure alone cannot. For pterosaurs, whose soft tissue biology remains poorly understood despite a large fossil record, reading their chemistry is a step forward.
Read More: 180-Million-Year-Old Ichthyosaur Found With 100 Teeth and Rocks In Its Stomach
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in iScience: Multi-staged mineralization and biomarker preservation in a 113-million-year-old pterosaur bone via local redox shifts in diagenesis
