Coprolites: The Serious Science of Fossil Poop

PALEODEX · 28 June 2026 · 6 min read

Fossilized dung sounds like a punchline. It's actually one of the richest windows into the deep past we have.

Let's get the giggles out of the way: yes, this is an article about fossilized poop. Now the serious part — coprolites are one of the most information-dense things a paleontologist can find. Bones tell you what an animal was. Poop tells you what it did: what it ate, how it digested, sometimes the world it lived in. Welcome to the most underrated corner of the fossil record.

Wait — fossilized poop?

A coprolite is exactly that: animal dung that mineralized over millions of years and turned to stone, keeping its shape and, crucially, its contents. It's a trace fossil — a record of behavior rather than a body part — which makes it a rare direct snapshot of a single meal, frozen at the moment of, well, exit. Inside, scientists find crushed bone, fish scales, plant fragments, even parasites.

A woman, some "bezoar stones," and a hunch

The story of how we figured this out is wonderful. In the 1820s, the pioneering fossil hunter Mary Anning noticed that odd, lumpy stones — then called "bezoar stones" — kept turning up in the belly region of the ichthyosaur skeletons she dug from the cliffs of Lyme Regis. When she broke them open, she found fish bones and scales inside. She suspected they were fossilized feces and said so to the geologist William Buckland. Buckland ran with the idea and gave the things a name: coprolite. Anning, often written out of the history of her own discoveries, had cracked it first.

What poop tells us that bones can't

Diet, directly. In 1998, the coprolite researcher Karen Chin and colleagues described, in Nature, the largest carnivore coprolite then known — over 40 cm long, almost certainly from a Tyrannosaurus rex. It was packed with the crushed bone of a juvenile plant-eating dinosaur. The detail that made it science, not novelty: a lot of that bone passed through undigested, telling us T. rex processed its food very differently from a modern crocodile. One fossilized dropping, one genuine behavioral insight. Herbivores have their own strange stories too — like a hadrosaur that seems to have eaten rotten wood on purpose.

The dung that rewrote plant history

Here's the one that still amazes me. In 2005, researchers studied 65-million-year-old coprolites from titanosaur sauropods in central India and found microscopic silica particles called phytoliths — plant cell fossils. Among them: grass. That was a problem, because grasses weren't supposed to have evolved yet. The poop pushed the known origin of grasses back by roughly 30 million years, and showed these giants browsed an entire salad bar of plants — grasses, conifers, palms and more. A single coprolite quietly rewrote a chapter of plant evolution.

Why this is peak PaleoDex

This is exactly the kind of unglamorous, real, sourced science we love. Coprolites aren't a gimmick — they're part of the fossil record, catalogued and studied like any bone, and they carry information nothing else can. The famous skeletons get the posters; the deep past hides in the overlooked stuff. That's the whole spirit of how we build PaleoDex: the real record, in all its strange detail. Browse the giants in the Fossil Library or travel their world on the Continental Drift map — just maybe wash your hands after this one.

Coprolite FAQ

What is a coprolite?

A coprolite is fossilized feces — animal dung that mineralized over millions of years, preserving its shape and often its contents. It's classified as a trace fossil, meaning it records behavior rather than being part of an animal's body.

What does the word "coprolite" mean?

"Coprolite" comes from the Greek kopros (dung) and lithos (stone) — literally, "dung stone." The geologist William Buckland coined the term in the 1820s after Mary Anning identified fossilized feces in ichthyosaur skeletons.

How do coprolites form?

Like other fossils, coprolites form when minerals (usually calcium phosphate or silica) replace or infiltrate organic material before it decays, hardening it into rock over a long burial. The process preserves the original shape and often the undigested contents inside. For the full chemistry, plus how paleontologists rule out an ordinary rock, see how coprolites form and are identified.

Are there human coprolites?

Yes. Coprolites aren't limited to dinosaurs — human coprolites, some thousands of years old, have been recovered from caves and archaeological sites and studied for ancient diet and DNA. We go deep on one famous case in human coprolites: ancient poop, ancient DNA.

What is fossilized poop called?

A coprolite. The term applies to fossilized feces from any animal, not just dinosaurs.

Sources

Strange topic, real science — sources below.

• A king-sized theropod coprolite — Chin et al., Nature (1998)
• Dinosaur coprolites & the early evolution of grasses — Prasad et al., Science (2005)
• Coprolite — Encyclopædia Britannica (Buckland & Anning)