Poop fossils show how molecules survive for millions of years

When people imagine fossils, they usually picture towering skeletons in museums or the fine imprint of a fern pressed into stone. These are striking, but they only tell part of the story. History often leaves its most vivid clues in unlikely places. One of those places is prehistoric droppings.

Fossilized feces, known as coprolites, might seem unremarkable, but they are tiny archives of life. They record what creatures ate, how ecosystems functioned, and what conditions shaped preservation after death.

A recent study led by Curtin University shows just how much power these humble fossils hold. The findings reveal how delicate molecules can survive for hundreds of millions of years, long after the creatures themselves have vanished.

Beyond the obvious fossils

The researchers examined coprolites dating back 300 million years – many of which were from the renowned Mazon Creek fossil site in the United States. This location is known for its ability to preserve ancient life in remarkable detail.

Scientists already knew the coprolites contained cholesterol derivatives. Those molecules pointed clearly to meat-eating animals. But a puzzle remained. Molecules that fragile should not have survived such immense spans of time. What kept them intact?

The team dug deeper into the chemistry and found an answer that upended earlier thinking.

Molecules preserved in fossils

The obvious suspect was phosphate minerals. These often stabilize fossil structures, so many assumed they also preserved biomolecules. That turned out to be wrong. The real guardians were tiny grains of iron carbonate scattered throughout the fossils.

Study lead Dr. Madison Tripp explained the significance of this finding. She noted that fossils don’t just preserve the shapes of long-extinct creatures – they can also hold chemical traces of life.

“But how those delicate molecules survive for hundreds of millions of years has long been a mystery: since phosphate minerals help preserve the fossil’s shape and structure, we might have expected these to also help preserve molecules – but we found instead that it was the iron carbonate that shielded the molecular traces inside,” said Dr. Tripp.

“It’s a bit like discovering a treasure chest – in this instance, phosphate – but the real gold is stashed in the pebbles nearby.”

Her words highlight how easily overlooked minerals can protect priceless chemical information.

Looking beyond one site

The team wanted to know if this process only occurred at Mazon Creek. They analyzed fossils from different species, environments, and time periods. The same pattern showed up again and again. Iron carbonate was doing the preserving.

Professor Kliti Grice, founding director of Curtin’s WA-Organic and Isotope Geochemistry Center, emphasized the importance of this consistency.

“This isn’t just a one-off or a lucky find: it’s a pattern we are starting to see repeated, which tells us carbonate minerals have been quietly preserving biological information throughout Earth’s history,” said Professor Grice.

The conclusion was clear. The preservation of biomolecules follows rules that can be recognized, not accidents that happen once in a while.

A new approach to fossil hunting

This discovery changes the way researchers think about fieldwork. Paleontologists often rely on chance, hoping to uncover a fossil that contains traces of ancient life. Now, they can be more strategic. Sites rich in carbonate minerals stand a much better chance of containing preserved molecules.

“Understanding which minerals are most likely to preserve ancient biomolecules means we can be far more targeted in our fossil searches,” Professor Grice explained. “Rather than relying on chance, we can look for specific conditions that give us the best shot at uncovering molecular clues about ancient life.”

The ability to predict where molecular traces survive reshapes the hunt for fossils and could speed up discoveries.

Broader implications of the research

The value of these findings extends beyond knowing what preserved a molecule. They give scientists tools to reconstruct entire ecosystems. Coprolites become more than traces of digestion. They become chemical records of interaction, decay, and environment.

“This helps us build a much richer picture of past ecosystems – not just what animals looked like, but how they lived, interacted, and decomposed,” said Professor Grice. “It brings prehistoric worlds to life in molecular detail.”

Through these molecular snapshots, paleontology shifts from static reconstructions to dynamic insights. Researchers can see how life once moved, fed, and broke down.

From droppings to discovery

The idea that fossilized droppings could hold such vast information challenges assumptions about what matters in the fossil record. Coprolites were once dismissed as curiosities, but this research places them at the center of molecular paleontology.

Tiny iron carbonate grains, unremarkable to the eye, act as protectors of life’s oldest molecular whispers. Thanks to them, fragments of ancient ecosystems survive in remarkable clarity.

By studying these grains and the coprolites they shield, scientists step closer to understanding prehistoric worlds as living, breathing systems rather than frozen relics. What once seemed trivial now becomes vital, proving that even the smallest traces of life can reshape our view of Earth’s past.

The study is published in the journal Geobiology.

Image Credit: Curtin University

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