A tan cylindrical mass with bits of plant material inside it sat on a hill in northwestern New Mexico, gently falling apart in an area known as the “Fossil Forest.”
“I was very excited,” Hunt, director of the New Mexico Museum of Natural History and Science in Albuquerque, recalls. “Your mind wanders off and you can imagine that the warm feces was left by a dinosaur that just walked behind the hill … You feel like you’re there.”
The notion of fossilized dung may draw wry smiles from some. But the researchers who study coprolites, as fossil feces are known, say these dietary waste products can tell us much about dinosaurs and other ancient animals.
Coprolites are the most rare of all dinosaur fossils. They belong to a group known as trace fossils. The class includes dinosaur tracks, regurgitalites (fossilized vomit), and cololites (think coprolite, trapped in the lower digestive tract).
A Little Respect, Please
English scientist William Buckland discovered the first coprolite in 1823, 20 years before dinosaurs were known to science.
But in the 180 years since, most paleontologists have paid coprolites scant attention. “They’re the Rodney Dangerfields of the fossil world,” Hunt concedes.
That may be changing, however. Experts say coprolites are garnering greater respect in paleontology circles. Some go so far as to say that paleo poop represents one of the more intriguing—albeit uncharted—fields of dinosaur fossil research.
“I think for a long time people saw them as ‘giggle fossils’ because they’re … unusual,” says Karen Chin, a paleontologist at the University of Colorado, Boulder and perhaps the world’s leading coprolite researcher. “It’s hard to draw paleobiological information from them. You don’t know, necessarily, who produced them.”
“But I think, like dinosaur tracks … they have really lent credence that there are a lot of things that we can tell from these [trace] fossils. But it takes a while to be careful enough to be able to draw the right conclusions.”
Michael Brett-Surman, a paleontologist at the Smithsonian Institution’s National Museum of Natural History in Washington, D.C., notes that coprolites provide a “direct link” to the diets of dinosaurs. (Brett-Surman does not study coprolites, but rather the lives of hadrosaurs, a type of duck-billed dinosaur.)
By studying such dietary evidence, scientists can learn much about the metabolism, physiology, and behavior of the dinosaur that produced it—even the environment the dino lived in.
“[Coprolites] were made by living, breathing, sweating dinosaurs,” Hunt says. “They can tell us things about that live animal that body fossils [such as bones and teeth] never can.”
Items found in coprolites produced by dinosaurs and other ancient animals include fossilized bone, teeth, fur, plant stems, seeds, pollen, wood chips, fungus, insects, larvae, dung beetle burrows, fish scales, shells, and microfossils of glassy marine organisms just 30 to 50 microns (one- to two-thousandths of an inch) in size.
Chin even allows that she is working on a coprolite found to contain fossilized tissue—a potentially exciting discovery. (Chin declined to provide more details, citing the protocols surrounding unpublished research.)
Chin, herself, made a big splash in scientific circles in 1998 when she published analysis of a king-size, meat-eating dinosaur coprolite unearthed in Saskatchewan, Canada. Based on its size (2.4 liters/2.5 quarts), age, the presence of bone chips and other clues, Chin concluded that the most likely candidate to produce such a copious deposit was a Tyrannosaurus rex.
In many respects, Chin’s work is akin to forensic pathology. Working in her lab, she uses chemical analysis to tease secrets from coprolite samples. Chin often cuts samples into thin slices and examines them under high-powered microscopes.
Her early work as a naturalist for the U.S. National Park Service also informs her work, Chin says. (Moose scat, for example, varies in consistency throughout year, thanks to the seasonal availability of succulent forage.)
While investigating the king-size, Saskatchewan dinosaur coprolite, Chin consulted Greg Erickson, a paleobiologist at Florida State University, who analyzed the vascular patterns found in the fossil’s bone fragments. Erickson concluded that the prey animal was a sub-adult, plant-eating dinosaur.
In the case of another plant-eating dinosaur coprolite, found in Montana’s Two Medicine formation, Chin discovered a series of preserved burrows. Consulting with Canadian dung beetle specialist Bruce Gill, Chin confirmed that ancient dung beetles produced the smooth channels.
Grand Synthesis Elusive
Such discoveries may sound like small beer. But they are precisely the type of information that, piece by piece, paper by paper, fossil by fossil, year by year, accumulates into a large database of collective scientific knowledge.
Against such a background, a grand synthesis becomes possible on the heels of other discoveries. One recent example is the association of modern birds as the evolutionary descendants of certain dinosaurs.
When it comes to dinosaur coprolites, however, such riveting stories of scientific discovery are few and far between.
The main reason for this is that coprolites are among the rarest dinosaur fossils of all. “It’s easier to find a big, fat diamond then it is to find a coprolite,” Brett-Surman, the Smithsonian paleontologist, says.
“That’s why we get so excited when we find dinosaur feces,” Chin says.
Part of the problem lies in knowing what to look for when fossil-hunting in the field. Or in the parlance of paleontologists, having the right “search image.”
To date, fewer than a dozen coprolite types have been positively linked to dinosaurs. (Compare that to the hundreds of dinosaur species that have been excavated and named over the past 150 years.)
“We only talk about a dozen associations, if that,” Hunt notes. “Given how many dinosaurs we know and how much excavation and exploration we’ve done, it’s rather sad.”
Once a coprolite is found, questions mount. Perhaps the most existential: Is the fossil truly a coprolite?
“There a lot of things that people show me that I don’t really know,” Chin says. “And sometimes, even after tests, I may not be able to tell for sure.”
Other cases are more clear. Chin reportedly found a patently modern rabbit pellet masquerading as coprolite in one museum collection.
Given the limits of what the fossil record does and does not preserve (what Brett-Surman calls the “great filter of Mother Nature”) the most important question surrounding a coprolite is one that often can never be answered. Namely, who produced it?
“In many cases we may never know,” Chin says. Or as Brett-Surman observes, “Let’s put it this way. It’s easier to find out what the animal ate then who took the dump.”