A self-taught geologist and finder of prehistoric shark teeth, Roberto is the eyes and ears of world-­renowned paleontologists who share his obsession for the Carcharocles megalodon shark, which terrorized the sea between two million and 16 million years ago. Consumed with the geology of the Ocucaje Desert, this 50-year-old with an aristocratic Spanish heritage prefers a life of few possessions - some desertworthy garb and gear, books, a chess set, and a signed declaration from Peru's National Institute of Culture that names him an official protector of the Ocucaje. His home in Ica, 200 miles south of Lima, is decorated with satellite maps of the desert. Most of his megalodon collection is stored elsewhere - perhaps someday he'll open his own museum. Even so, Roberto considers himself a finder, not a collector.

I FIRST MEET ROBERTO a few miles from Ica at my hotel in Huacachina, a tiny palm-fringed lake surrounded by monstrous sand dunes. "So, how'd you hear about me?" he asks. "And why would a woman from New York City want to go 150 kilometers off-road to look for sharkies in one of the driest deserts in the world?" I blurt out: "When I was a little girl, my grandfather used to take me to a canyon in California, where we found fossils of fish and seashells. I was completely in awe of the fact that something millions of years old could still exist. My grandpa was the most fascinating man I'd ever met." Upon hearing this story, Roberto melts. And suddenly I realize that my entrée to the depths of the Ocucaje hasn't been a sure thing. "You've passed the test," he announces. "I will pick you up tomorrow morning at eight."