You are in the oceans of Europe, 180 million years ago.

The Jurassic sun beat down on the shallow, murky estuary, turning the water a hazy teal. In your diving suit, you floated silently, scanning the seabed for ammonites, unaware that you were in a “death zone”.

The water grew quiet, and a sudden shadow passed beneath you, too fast and too sleek to be a slow-moving plesiosaur. You froze.

Through the cloudy water, a shark emerged—about six feet long, with a dark, mottled back that vanished into the gloomy depths. You saw the distinctive, rigid dorsal spines—one in front of each dorsal fin—cutting through the water like obsidian blades.

It wasn't a monster, but it was perfectly designed for this environment. The shark turned, its massive, dark eyes locking onto you with cold intelligence, looking for an easy meal…