Fecund Feces




T. rexcrement. This 2.4 liter object was deposited 65-million years ago in Saskatchewan. From the crunched-up dino bones it contained, scientists figure it's the daily business of a Tyrannosaurus rex.
Courtesy Karen Chin and USGS.


Like wildlife biologists, archeologists find feces fascinating.



POSTED 3 MAY 2001You wouldn't think feces would fossilize. In fact, you'd admit you don't think much about feces at all. Same way around here: We Why Filers are pretty much a flush-and-forget crew.

a photo of an enormous-looking coproliteBut Karen Chin thinks so much about fossil feces that she can even pronounce the phrase. In fact, the Stanford University post-doc waxes wistful about waste. Fossilized excrement, she says, "can tell us a lot about population, health, distribution and diet."

Like anyone who studies repulsive stuff, Chin has a ready rationale. "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, when you think about it. 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. That's the technical term for "squoze out."

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 photo of a slice of coprolite (fossilized exrement)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.

Having read this far, do you now promise to focus more fervently on fossilized feces? If so, you'll know the right answer when Chin (a putrid punster whose quips have been purposely perpetuated previously) asks: "Does fecal matter?"

-- David Tenenbaum


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