You are in the oceans of North America, 85 million years ago.

The water of the Western Interior Seaway was murky, filtered sunlight barely piercing the greenish gloom. You were holding your breath, partially hidden behind a shelf of limestone, my lungs burning, observing the prehistoric carnage.

The shadows moved. Not a shark, not a mosasaur. It was faster, smaller—about five feet long—but a nightmare of sharp, glittering blue armor. A Bananogmius swam past you.

It looked like a massive, deranged, Cretaceous angelfish. Its body was extraordinarily thin and deep, rising to a jagged, exaggerated dorsal fin that sliced through the water like a weapon. Its scales glinted with a dull, silver-gray sheen.

It wasn’t alone. A school of ten, acting with eerie unison, began foraging among the seafloor sponges. You watched one turn its head, the side-view showing that ridiculous, blade-like body… and dive downward towards your direction…