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POSTED 3 MAY 2001You wouldn’t think feces would fossilize. In fact, you’d admit you don’t think much about feces at all.
But Stanford University post-doc Karen Chin waxes wistful about waste. Fossilized excrement, she says, “can tell us a lot about population, health, distribution and diet.” “There’s a certain intrigue about going out to dig up ancient animals, but some people don’t think what I study is all that romantic. But fossil feces can be just as interesting as the study of animals.”
Wildlife biologists, she notes, make no apology for studying scats — the feces of live animals. Similarly, coprolites, as archeologists term fossilized feces, convey information about the lifestyles of the dead and buried.
Scat that had nine lives
How does something as soft and ephemeral as a turd even become a hard fossil? Before getting fossilized, feces can be eaten, digested by microbes, or washed or blown away. In fact, Chin lists nine separate perils that can prevent a scat from becoming a fossil.
Most feces do disappear before fossilization, which is probably a good thing. But if even a small percentage of feces gets fossilized, that’s enough to leave a substantial record. After all, Chin says, “an animal only dies once.” But it’s gotta go every day of its life…
When sliced into thin sections and examined under a microscope, coprolites may contain seeds, leaves, wood, mollusks, bones or teeth. The list, obviously, includes lots of the indigestible crud that carnivores devour.
Carnivore dung is also chemically conducive to fossilization, Chin adds. Bones contain calcium, which can combine to form calcium phosphate, the major chemical that, through the process of permineralization, turns soft feces into hard fossils.
The presence of both calcium phosphate and partly digested food remains are diagnostic for coprolites, which generally have that sausage shape characteristic of extrusion.
Chin says the absence of calcium phosphate and indigestible crud reveal that many “coprolites” sold at rock and gem shows are bogus.
Caveat excrement emptor.
A thin slice of coprolite shows fish teeth and fish vertebrae. Guess what this animal ate?
Courtesy Karen Chin.
As one of the world’s few experts on coprolites, Chin was called in to examine a titanic turd (more than 2.4 liters in volume) deposited in Saskatchewan near the end of the dinosaur age. The scat contained the bones of a young, herbivorous dino — an itsy-bitsy critter no bigger than a cow. Although carnivorous dinos didn’t masticate their food as mammals do (their teeth did not mesh well enough for that), the immense crushing pressure of a Tyrannosaurus rex jaw could have busted the bones, explaining the bone chunks.
Who dung it?
Identifying what Chin calls the “poopetrator” is probably the most difficult part of studying coprolites. While Chin observes that you can never know for sure, the giant T. rex poop shows that guesses are based on the fossil context, and on the size and contents of the coprolite itself.
– David Tenenbaum
