Digging Into Doo-Doo

Sometimes the best bundle of information about an animal’s life is found in what it left behind — literally from its “behind” (and, generally, after a good meal).

Yes, we’re talking about poop — or, to be more polite, “stool,” “dung,” “feces,” or “excrement.” Call it what you will, but for many paleontologists, the scientists who study life long ago, finding poop from a dinosaur, saber-toothed cat, or even tiny sea snail is like hitting a jackpot. They eagerly slice and dice a pile of it to learn about the animal and its life.

This probably would be a good time to note that the poop is fossilized, hard as a rock, and, thankfully, no longer stinky or gooey. In fact, fossilized feces can be so beautiful — full of little bits of plants, shells or winding insect burrows — that jewelry makers polish slices or beads of it to create gorgeous necklaces, earrings, or bracelets.

Considering all the poop that animals dump during their lives, fossilized feces is quite rare. Usually animal’s excrement — the remains of food that wasn’t digested — just decomposed, breaking down and fertilizing the ground underneath. Sometimes smaller animals would feast on the poop. (Yeah, gross, but it’s actually nutritious.) And on rare occasion, the animal’s feces would quickly get covered by mineral-rich sediment or water and over a really long time harden into a fossil, creating what scientists call a “coprolite” and other people call a “dung stone.” (Both terms are right. The fossil gets its name from the Greek words kopros, which means “dung,” and lithos, which means “stone.”)

Coprolites are a type of trace fossil, one that records what the animal did, instead of the kind of fossil, like a dinosaur skeleton, that forms directly from the animal’s remains. That kind of fossil is called a body fossil.

Some paleontologists focus their careers on examining coprolites. Unlike a fossil skeleton, which shows what an animal looked like, coprolites give a wealth of other information about an animal’s diet, environment, and even behavior, paleontologist Karen Chin told the public radio program Science Friday.

Coprolites may contain fossilized bits of plants and animals, such as fish scales, shells, bones, or even muscle tissue from the animal’s prey. They reveal whether the animal that produced the poop was a herbivore (plant-eater), carnivore (meat-eater), or omnivore (eater of both plants and animals).

Or even a cannibal. Not long ago, for example, scientists discovered that a prehistoric shark called Orthacanthus ate its own young. They found a distinctive spiral-shaped Orthacanthus coprolite that contained an equally distinctive tiny Orthacanthus tooth. News of their gruesome discovery was a big deal and published in the scientific journal Paleontology and reported by the BBC.

Coprolites even revealed why the famous Tyrannosaurus rex may have been constantly on the prowl for its next meal. It didn’t absorb all the available nutrition from its meals, leaving a lot of undigested flesh and bone in its poop. That meant that the massive dinosaur needed to eat a huge amount of food to get enough energy to keep going, according to Smithsonian Magazine. Poor thing was probably hangry all the time.

It isn’t always easy to identify which animal produced the poop — after all, the food traveled down the animal’s digestive tract and then the coprolite was battered by maybe millions of years of erosion and weathering, paleontologist Karen Chin said. In addition, fossils of the animal that went Number 2 are not usually found in the same location as the pile of poop.

But there are exceptions. Some coprolites — such as those from some prehistoric sharks and other fishes — have really distinctive shapes that give away what kind of animal produced the feces, according to the Natural History Museum in London. Some sharks’ intestines had spiral valves that created similarly shaped grooves in shark feces. Other prehistoric sharks and primitive fish produced scroll-shaped feces that looked like a rolled sheet of paper, according to a study published in Science Reports.

In addition, especially in more recently formed coprolites, some scientists have been able to find enough genetic material to identify the animal that produced the feces as well as the specific kinds of animals and plants it ate, according to a study reported by Science Direct.

Even when scientists can’t identify the animal responsible for the pile of poop, the coprolites are still extremely valuable. Besides revealing the animal’s diet and feeding behavior, the fossils also provide information about the animal’s environment: whether the animal lived in water or on land, what other organisms lived around it, and even — based on how the poop was preserved — what the surroundings were like, paleontologist Karen Chin said. By studying many coprolites, scientists can figure out what ate what and reconstruct prehistoric food webs.

Coprolites come in all shapes and sizes, from teeny insect droppings to a 20-pound T. rex turd. While many coprolites look pretty much like rocks, others look so much like a freshly deposited pile of poop that you’d jump away if you saw it lying on the sidewalk. But maybe that “eww” factor is part of their appeal. Coprolites actually are favorites of fossil collectors. One enthusiast collected more than 1,200 coprolites — so many that he was able to open his own museum, the Poozeum!