Those teeth turned out to be as important as they are terrifying. Because penis worms are, well, pretty flaccid, they don't stand up well to the rigors of time. It's hard to find a fossil of a squishy-bodied animal, and during the Cambrian period -- when penis worms like the Ottoia were slithering about the planet -- most living creatures were fairly boneless.

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Knowing that these particular critters had tons of teeth means that researchers can look for those bony fragments in lieu of complete fossils. But the teeth are tiny, so researchers often mistake them for other things. Or if they find them, they might not know which penis worm's maw they're looking at.

So a group of intrepid penis worm researchers have set out to make an intense dental study of the penis worm. Their findings were published Wednesday in the journal Paleontology.

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"Taken together, our study has allowed us to compile a 'dentist's handbook' that will help paleontologists recognize a range of early teeth preserved in the fossil record," lead author Martin Smith of the University of Cambridge said in a statement.

"As teeth are the most hardy and resilient parts of animals, they are much more common as fossils than whole soft-bodied specimens," he explained. "But when these teeth - which are only about a millimetre long - are found, they are easily misidentified as algal spores, rather than as parts of animals. Now that we understand the structure of these tiny fossils, we are much better placed to a wide suite of enigmatic fossils."

By using high-resolution imaging techniques to classify the Ottoia teeth, they were also able to distinguish the teeth of several other ancient penis worm species.

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Today penis worms only persist in extreme environments, so they don't occupy much space. But back in the Cambrian, they flourished. And thanks to the new dental research, it's possible that paleontologists will uncover new species that have been lost to time.