You are in the freshwater swamps of Europe, 320 million years ago.

The air was heavy, humid, and thick with the scent of rotting vegetation and spore-heavy ferns. Your paddle dipped into the black water of the Carboniferous tributary, a narrow waterway cutting through a dense swamp forest filled with giant arthropods and early amphibians. The water was only about four feet deep here, shallow enough to see the muddy bottom.

Suddenly, you spotted movement in the water. A massive shadow has detached itself from the tangled roots on the bank. It wasn’t a log. It was long—twenty feet at least—with pectoral fins that moved almost like legs, propelling its heavy, scaley body upward from the sediment. Before you could react, the shadow swam past your canoe and violently smacked the hull with incredible force, nearly knocking and flipping the canoe and you over. The surface twenty feet away exploded.

It wasn't a splash; it was a detonation of mud and water. A dark, muscular mass surged from the reeds, larger than any crocodile. Its head was enormous, holding eyes that stared with cold, hungry intent. The most terrifying part was the teeth—shining fangs the size of your forearm, jaggedly arranged in a mouth that could swallow you whole.

As its jaws snapped shut just inches from your foot, sinking into a submerged log with a sound like shattering timber, you realized this wasn't just a fish—it was the apex predator of this ancient, humid world, and you are unlucky to be part of its menu.