You are in the deep oceans of North America, 460 million years ago.

The water pressure at 500 meters was immense, a crushing weight that your submersible’s titanium hull barely registered. You were scanning the edge of a deep, ancient reef, looking for trilobites and sea scorpions in the gloom, when your spotlight caught an enormous shape that redefined the term "monster."

It was a Cameroceras.

Through the thick quartz glass, you watched it glide—not swim, but move with a slow, deliberate majesty. A massive, straight cone, easily 19 feet long, was its shell, patterned in muted browns and grey to blend with the seabed. It looked like a living ice cream cone, armored and archaic.

At the opening of the massive, rigid shell, a bouquet of thick, muscular tentacles coiled, sensing the environment. In the center, a dark, sharp beak—large enough to crush armored prey—remained partially open. As it passed, its enormous, dark eye, easily as large as your own head, turned to fix on the submersible. It didn’t seem afraid; it seemed indifferent, a titan of the Ordovician ocean 460 million years before sharks or whales existed.