One large oblong fossil poo surrounded by eight poops on smaller rocks. Some of the smaller poops are stringy, some are more circular.
Coprolites come in all shapes and sizes.

NPS photo

Coprolites are fossilized poops. The word coprolite comes from the Greek words kopros, meaning dung, and lithos, meaning stone.

Although the butt of many jokes, coprolites can be very helpful expanding our understanding of Fossil Lake. Initially, scientists thought the fishes lived in tributary streams and their bodies floated into the lake after death. Coprolites show that is incorrect. If they were pooping in the stream, the flowing water would break the delicate coprolites apart before they made it to the lake. To preserve delicate feces, the fishes had to be living in the calm waters of the lake when they pooped.

It is not possible to determine which animal left behind which poop, although we can make some guesses. With the abundance of fishes in the lake, we can assume the stringy coprolites that resemble modern fish poo came from fishes. Sometimes poops contain bones and teeth which can be used to identify the prey, though the predator’s identity remains a mystery. We can narrow down the pooping culprit by size, for example, an 8-inch-long coprolite likely came from a crocodilian or turtle and not a 5-inch Knightia eocaena.
Knightia eocaena with colonite. A long, thin fish fossil with a forked tail. There is an oblong shape inside the fish in the middle, right at the bottom.
Knightia eocaena with colonite, catalog number FOBU17646

NPS photo

The only time it is possible to tell whose poop it is for certain is when it is still inside the body. In this case it is known as a colonite because it is preserved in the colon. The Knightia eocaena to the left contains a colonite.

See hundreds of coprolites during your visit to the park in the most appropriate location: the restrooms.

Before your visit, preview our museum exhibits.

Last updated: January 31, 2024

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