You are in the oceans of Europe, 418 million years ago.

The water of the Silurian sea was warm, shallow, and impossibly clear, allowing the sunlight to dance across the sandy bottom. You were observing a group of Cephalaspis—small, jawless fish—rooting for food in the mud, their armored heads gleaming.

Suddenly, the water seemed to darken. The small fish froze, then darted away in a frantic panic.

Out of the deeper, murky water, it surged. It was massive—easily seven or eight feet long, dwarfing everything around it. It moved with terrifying efficiency, utilizing its paddle-like tail to propel its segmented body forward while holding its terrifying pincers in front of its head. Those claws were nearly half the length of its body, thick and fortified with sharp teeth designed for breaking armor.

Its compound eyes, perched on the edge of its head, seemed to lock onto a slow-moving target. The Pterygotus didn't waste time. It snapped its great claws with a sound that felt like thunder underwater, snapping up an unfortunate fish in a swift, brutal motion.

You stayed perfectly still as the giant arthropod settled onto the seabed, its long swimming legs resting near the seafloor, waiting for another animal to pass by to feast on…