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coprolite fossils
Coprolite from Madagascar, presumed to have been left by a giant turtle.
So what is a coprolite, anyway?
To put it simply: coprolites are the petrified feces of some long ago animal (or even human).
Coprolites form in much the same way as any other fossil - the original organic material is infused with water containing dissolved minerals, and as the minerals crystallize, the original material is slowly replaced by stone.
Most people, when handed a coprolite for the first time, go and sniff it as their first impulse. But it smells of nothing but stone, because that's all it is now, technically speaking.
Coprolites are at a disadvantage from the start in the fossil-forming process. Generally speaking, the quicker to decay an object is, the less likely it is to successfully fossilize. Fossilization takes time, and if the whole thing rots before it can finished, well, no fossil [1]. That's why hard and durable objects, such as bones and teeth, are much more common fossils than soft tissues, or coprolites.
Coprolites were first identified as what they actually are, by a woman named Mary Anning (21 May 1799 – 9 March 1847). Mary Anning was a fossil collector and paleontologist from southern England, and noticed these odd stones inside the abdominal areas of the ichthyosaur fossils she was collecting. When she broke them open, she noticed they had fragments of fossilized fish bones and scales. .
in 1829, Anning's observations led a geologist named William Buckland to propose that these stones were the digested remnants of the dinosaurs' last meals, and he gave them the name of coprolites.
Those fossil fragments inside coprolites contain a wealth of scientific information, for anyone who really wants to look closely. The kinds of fossils contained in the coprolite can tell us a lot about the environment the creature was living in, by what it found in the area to eat. It also reveals the creature's preferred food sources, such as whether it was an herbivore or a carnivore, and sometimes it will even reveal what parasites plagued its creator. And, yes, we learn a lot about its intestinal systems. That's pretty much a given.
The challenge, of course, is in determining exactly which species of creature left a particular coprolite behind. In some cases, when there are a lot of fossilized remains of a particular animal around, it's easy to make a good guess. And in some cases, as with Mary Anning's fossils, the coprolites were petrified while still within the animal's body. But with a more isolated coprolite specimen, it can be very difficult.
Early human settlements left the occasional coprolite as well, so they have archaeological value as well as geological value. As it turns out, we can learn about our own history from them. A human coprolite found in a cave in Oregon revealed the existence of a long-lost 13,000-year-old society [2].
And a research team from the University of Colorado, studying an ancient Anansi settlement in Colorado known as Cowboy Wash, uncovered human remains showing what they believed to be evidence of cannibalism. They tested a coprolite found nearby, and discovered it contained a protein only found in human muscle tissue, confirming their theory [3].
Oddly enough, coprolites from dinosaurs and other prehistoric beasts are often used in jewelry. Due to the mineralization, many of them have bright and beautiful coloration. And, well, you get a great answer to give when someone says, "Ooh, what a pretty necklace! What stone is that?"
Some people may think coprolites are disgusting, but like any other fossil, they're also windows into a lost and wondrous past on this planet.
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Sources:
[1] http://discovermagazine.com/1996/jun/whatthedinosaurs786
[2] http://www.foxnews.com/scitech/2012/07/12/fossilized-human-feces-hints-at-long-lost-13500-year-old-west-coast-culture/
[3] http://www.smithsonianmag.com/people-places/anasazi.html?c=y&story=fullstory