Two million years ago, it wasn't safe to go in the water, thanks to a predator the size of a Greyhound bus. These days, you have to search the Peruvian desert to get face-to-face with the granddaddy of Jaws.
"Roberto, Roberto, come see!"

I'd made a remarkable discovery in the Ocucaje Desert, 12 miles inland from Peru's southern coast, but my guide was a quarter of a mile away, relieving himself in a gully. I jumped up and down, screamed, and did a few cartwheels, which made my head swirl, but still no Roberto. Here in one of the oldest and quietest places on Earth - a wondrous desert of tiered escarpments, sedimentary rock, and level stretches between Precambrian volcanic mountains - no one else would hear my squeals. Waiting for Roberto to reappear, I paced back and forth across a fossil-embedded­ steppe, a broken section of the ocean floor that was thrust 2,600 feet above sea level 12 million years ago. When he finally returned and saw my big surprise - a three-inch-long fossilized tooth from a megalodon shark - a beaming Roberto said, "Pachamama ["earth mother"] sent me to the water closet­ so you'd find this gift."

Three weeks earlier, I'd read an online posting about Roberto Penny­ Cabrera, and called him to find out more about the ocean's largest-ever predator. "Forget Jaws. The megalodon was more than twice as long as a great white shark, much larger than a Greyhound bus," he told me. "With an enormous mouth 11 feet high and nine feet across, it could break a whale in two with one bite." Roberto's enthusiasm for "sharkies" was endearing. Later I learned he was actually saying "shark teeth" so fast that the words ran together, but by then I'd grown fond of the term and chose to hear it that way.