Fossil Fecal Forensics

Saturday, May 4, 2019

Credit: Luke Groskin

While the fossilized skeletons stick out in images from books or movies in our mind as the primary evidence that dinosaurs and other prehistoric creatures walked the earth, they can’t tell us the whole story of how extinct organisms lived. For that, you need fossilized poop, called coprolites.

“These little magic packages can provide really special perspectives on ancient life,” says Karen Chin, an associate professor of geological sciences at the University of Colorado, Boulder.

“Skeletal fossils don’t always tell you too much about the behavior of animals,” she says. “In addition to diet, [coprolites] can also tell you about what organisms might have been living along with the animal that defecated, and coprolites can also tell you about the conditions under which they were preserved.”

Everyone poops. This adage even applies to prehistoric creatures—from crustaceans to dinosaurs—that lived on land and in the sea. Over the course of any given organism’s lifespan, piles of poop were produced countless times. Unfortunately for those seeking fossilized examples of excrement, poop just doesn’t fossilize as well as bones or shells. Ancient feces fossilized only if a mineralizing agent covered it relatively quickly after it was produced. If mineralization was successful and decomposition was avoided, then feces could fossilize, forming a coprolite. 

While it may seem like a less glamorous side of science, the study of petrified poo is incredibly important.

When Dr. Chin began studying these coprolites, she found they contained unexpected surprises. Coprolites from herbivorous dinosaurs had more than just leaf matter inside of them. She found dung beetle burrows, snail shells, and tiny pieces of conifer wood. The pieces of conifer wood were no ordinary pieces of wood—they had actually been rotting before being ingested. This is incredibly intriguing as rotting wood isn’t on the diet of many organisms, even herbivores such as these dinosaurs.

In Choteau Mountain’s Two Medicine Formation in Montana and the Kaiparowits Formation in Utah, fossil body parts, coprolites, and trace fossils, which are fossilized indicators of an organism’s presence, can be found. These two formations contain fossils dating back to the late Cretaceous period, which is the period just before dinosaurs went extinct. Famous dinosaurs such as triceratops and Tyrannosaurus rex roamed the area, and fossils of these species along with many other creatures, are found in the Two Medicine and Kaiparowits Formations.

For this activity, you’ll step into the shoes of Dr. Karen Chin to see what you’re able to gather from coprolite samples from the Two Medicine and Kaiparowits Formations. You’ll try to answer the same question Dr. Chin pondered: Why is there wood in fossilized poop created by herbivorous dinosaurs?