What fossilized poop can teach us about dinosaurs

Karen Chin in the University of Colorado Museum of Natural History, where she is the curator of paleontology. She is also a professor of geological sciences at the University of Colorado, Boulder and a leading expert on fossilized dinosaur feces. Casey A. Cass/University of Colo hide caption

toggle caption Casey A. Cass/University of Colo

As a graduate student, Karen Chin worked on a dinosaur dig site in Montana with the renowned paleontologist Jack Horner. Her job was to cut thin sections from fossilized skeletons in order to analyze them under the microscope.

But it wasn’t the bones that caught her attention.

“I learned that somebody had found fossilized feces, and I thought that was just the weirdest thing,” she recalls. So she asked to make a thin section of the feces. “And when I looked through the microscope, I could see plant cells that were ingested 75 million years ago by a dinosaur. And it blew my mind because I thought, ‘Man, this is how you can learn about interactions between dinosaurs and plants and other organisms.'”

Chin is now one of the world’s leading experts on dinosaur feces—known scientifically as “coprolites,” stemming from Greek that means “dung stones” or “poop rocks.” She’s even the subject of a recent children’s book called The Clues are in the Poo.

Recently, we went to visit her at the University of Colorado, where she is a professor of geological sciences and the curator of paleontology, to find out what getting hands-on with fossilized feces can teach us about dinosaurs.

The first thing you notice on walking into Chin’s office is that petrified poops are everywhere. They’re in shallow boxes covering every surface and filling up shelves, cabinets and drawers.

“They just look like black rocks,” she explains. “They don’t have the sausage shape that you would expect to see of fossil feces. They’re kind of angular.”

Karen Chin excavating a dinosaur coprolite at the Kaiparowits Formation of Southern Utah. Karen Chin hide caption

toggle caption Karen Chin

That’s because, well, they had a hearty distance to fall from the dinosaur’s butt to the ground — and so likely broke apart on impact.

As for the size of dinosaur dung, Chin says none approach the Jeff Goldblum-height heaps seen in Jurassic Park. The biggest she has examined was six liters — a little smaller than a basketball.

“When I saw the movie, I thought that was rather humorous,” she says. “But it actually made sense because if you have a dinosaur in a zoo, they’re going to be producing so much dung. And what are the zookeepers going to do with it but pile it up in one place, so somebody could cart it off later?”

She says sometimes she can determine the identity of who dung it by nearby skeletal remains. But oftentimes the identity of the poopetrator remains a mystery.

“As a paleo-ecologist, it may not be the most important thing to know exactly who produced it,” says Chin. “If you can tell who is eaten and think about some generalized food webs in the ancient environment, you can get a feeling for what that environment was like. And this is another reason why I like coprolites so much, because they’re basically like receipts of transactions of carbon resources that are traveling through an ecosystem.”

A coprolite specimen in the field. Karen Chin hide caption

toggle caption Karen Chin

Chin has made a number of discoveries over the years that tell us about these ancient food webs and the dining behavior of dinos — things we often can’t learn from their skeletons.

The first was that dung beetles, long thought to have evolved with mammals after the fall of dinosaurs, were in fact around in the Cretaceous Period and happily burrowing into dinosaur patties in order to feed baby dung beetles.

Another find was that the tyrannosaurs, instead of being dainty eaters that picked meat from the bone like some scientists had hypothesized, gobbled up their prey, bone and all. It’s a conclusion Chin could make after finding bone shards and undigested meat in their coprolites.

“A tyrannosaur would have had a skull about three-feet long,” she says. “They couldn’t chew properly, so they would have grabbed and swallowed.”

One of her favorite discoveries came from finding large amounts of digested wood in the dung of herbivorous dinosaurs. It was perplexing because herbivores today can’t digest wood due to not being able to break down the tough glue-like substance called lignin that holds wood cells together. But Chin was clearly seeing broken-down wood in the dung of plant-eating dinos, along with, oddly, the shells of crustaceans.

So her idea was that maybe they weren’t eating healthy trees at all, but rotting wood.

“White rot fungi can actually destroy the lignin, and if they do that, that increases the digestibility of wood 30-to-60 percent,” she says. “So this meant these dinosaurs had been feeding on rotting wood. It was really surprising. You just don’t hear of that behavior in modern animals.”

At least, Chin says, not in the large mammals scientists often use as stand-ins for dinosaur feeding habits, like elephants and rhinos. But, then again, dinosaurs weren’t mammals. They were a lot more like their modern-day descendants: birds. And some seed-eating birds start eating insects when they’re laying eggs to get calcium to produce shells and protein to support the yolks.

Karen Chin at the Kaiparowits Formation of Southern Utah, where she discovered that herbivorous dinosaurs munched on rotting wood and all the crustaceans, worms and other creatures inside when they were reproducing, in order to gain protein and calcium for their eggs. Karen Chin hide caption

toggle caption Karen Chin

“So my hypothesis was that because we found these coprolites in the nesting grounds of dinosaurs, that the dinosaurs had to change their diet when they were reproducing,” she explains. “It seemed like, boy, if you’re a 25-foot-long duckbill dinosaur, and you suddenly need to get a lot of protein, you’re not going to be like a T-Rex chasing after animals. But you could find a predictable source of protein in rotting wood in the form of the invertebrates, insects, crustaceans, worms — all kinds of things that would be hanging around rotting wood.”

So the next time you think of feces as being nothing but a smelly waste … think again.

“This is telling us about eating interactions between organisms, about recycling processes,” says Chin. “When you’re holding a piece of fossil poop, that really shows us how dynamic life has been — not only today, but in the past.”

Interested in learning more ancient or scatological mysteries of science? Email us at [email protected] — we might cover it on a future episode!

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This episode was produced by Berly McCoy, edited by Rebecca Ramirez and fact-checked by Brit Hanson. Maggie Luthar was the audio engineer.