CU paleontologist Karen Chin reconstructs the physical and social world of the big dinosaurs — in part by teasing out who ate whom.
How do you describe what you do?
My research focuses on trying to reconstruct what Mesozoic ecosystems were like. That’s the time when the big dinosaurs lived. I say ‘big dinosaurs’ because birds are still here, and birds are dinosaurs. A lot of the rock deposits I work on are around 75 million years old.
What sorts of questions are you asking?
Many of the specimens I study are fossil feces, which provide evidence for the feeding activities of ancient animals. Oftentimes dinosaur scientists focus on fossil bones and reconstructing what animals looked like, which is extremely important. But I like to look at the interactions of dinosaurs with the other, less charismatic organisms that they lived with. I’ve studied things like dung beetles and snails that fed on dinosaur dung and beetles that fed on dinosaur bones. Most recently we found some burrows that may have been made by parasites inside the gut contents of a dinosaur.
The first question I ask is, what is the evidence that a specimen is actually fossil feces? This might be the presence of chopped up dietary residues; it can be the presence of distinctive animal burrows; it can be the chemistry. The second question is, who might have produced it? For that, we look at the paleontological context — what bones are found in the same horizon? And then the third question is, if this is a coprolite [fossilized dung], what can it tell us?
Where are we finding dinosaur feces?
Coprolites have been found probably on every continent. Whether they’re big enough to confidently attribute to dinosaurs is another question.
Of the coprolites that you are most confident are dinosaur coprolites, what parts of the U.S. or the world do they tend to show up in?
In the Rocky Mountains. Montana, Utah, Colorado, Wyoming. Texas, even. I’m pretty confident that there are coprolites in other places. But they’re really challenging to recognize.
Are there particular dinosaur species you have found most useful?
Carnivore feces tend to preserve much more easily than feces from herbivores. This is counterintuitive, because there have been far more plant-eaters throughout the history of life. But there is something in the carnivore diet — the chemistry of the food can be conducive to preservation of the feces. And the most common coprolites are those from aquatic animals, like fish, crocodilians, turtles. Feces are most easily preserved if they are rapidly buried. Thus, dinosaur coprolites tend to be rare. I could probably count on two or three hands all of the herbivorous dinosaur coprolite deposits in the world that I know of.
What are some of the practical challenges you face in your work?
A lack of well-preserved fossils. You could have tons of coprolites, but if they’re poorly preserved, you’re not going to find interesting things in them!
At what point are you satisfied that, yes, this is a coprolite?
When there are multiple lines of evidence. These might include paleontological and geological context. The presence of chopped up possible dietary residues. Chemistry. The presence of activity from organisms that were feeding on the feces.
What sorts of tools do you use most?
My best tools are my microscopes. I have microscopes that I use to look at the surfaces of things. And if there is enough material and I have documented the specimens very carefully, I will cut them and make thin sections so that I can look at them with my transmitted light microscope and try to recognize cell structures of things that were eaten. I also do a lot of chemical analyses.
What do you do outside of work?
I’m an avid gardener and plant collector. I have a garden and probably have close to 100 plants inside the house. They take a long time to water and care for. Orchids, cactuses, bromeliads and other tropical plants.
Condensed and edited
Photo by Casey A. Cass