You are in the oceans of Europe, 245 million years ago.

The water of the Triassic Tethys Ocean was warm, but a sudden chill ran down my spine as the sunlight above was blocked out. You were holding onto a rocky outcrop, observing a shallow reef, when the silence was broken—not by sound, but by a shift in pressure.

A shadow, immense and eel-like, glided from the deep blue into the light.

Cymbospondylus. It had to be nearly 10 meters long, its body a dark, mottled slate color, lacking the dorsal fin of modern sharks, undulating with a powerful, slow grace. Its head was relatively small compared to its enormous body, but the jaws were long and lined with hundreds of small, sharp, conical teeth designed for snatching cephalopods and fish.

You froze, knowing that while this ichthyosaur usually targeted cephalopods and smaller reptiles, an object your size would be a trivial snack. The giant didn't seem to notice you at first, its gaze focused on the water below. Its eye, huge and reinforced with a ring of bone for deep diving, focused on something, then snapped toward you.

It circled once, a massive, muscular serpentine form, its long, eel-like tail maneuvering it with surprising agility despite its size. The creature made a slow, deliberate lunge—a warning, perhaps, or a test…