The beaches were deserted near Santa Cruz, California, on December 23, 2007. Temperatures were cool for Cali standards, and the wind whipped unpleasantly across the sandy expanse.

But that didn't stop paleontologist Robert Boessenecker from avidly trolling the chilly shores. A senior at Montana State University at the time, Boessenecker was on the hunt for fossils, and he soon found his prize: a dark greenish blue tooth the size of his hand—“about as big as they come,” he says—peeking out of a cliff.

This rare find came from the ancient Otodus megalodon, the largest shark to ever glide through Earth's oceans. Though movies continue to stoke the conspiracy that these nearly 60-foot-long beasts still lurk in the inky depths, the