You are in the oceans of North America, 75 million years ago.

The water of the Western Interior Seaway was warm, clear, and blindingly bright, just 30 feet below the surface. I was hanging in the blue, holding my breath, when a shadow suddenly cut across the sun-dappled floor.

Something was moving fast beneath you—not the slow, heavy cruise of a mosasaur, but something agile and acrobatic. A pair of large, dark eyes appeared, watching me intently.

It was a Dolichorhynchops. It was beautiful, with a sleek, dolphin-like body roughly 10-15 feet long, punctuated by a disproportionately long, slender snout filled with interlocking, needle-like teeth. It didn't fear me. Instead, it circled, moving with surprising speed. It seemed to fly through the water using its four long, paddle-like flippers, operating more like a marine bird than a reptile.

It wasn’t alone. Three to four more individuals appear out of the blue, slowing down to circle you without effort, their eyes watching you with curious intent. You could hear the faint "click" and "chirp" of them communicating—a haunting, high-pitched chatter in the blue void. You held your breath, a tiny, fragile visitor in their world…