In 1993, Alaskan artist and paleo-shark enthusiast Ray Troll stumbled upon the weirdest fossil he had ever seen--a platter-sized spiral of tightly wound shark teeth. This chance encounter in the basement of the Natural History Museum of Los Angeles County sparked Troll's obsession with Helicoprion, a mysterious monster from deep time. In 2010, tattooed undergraduate student and returning Iraq War veteran Jesse Pruitt became seriously...