You are in the deep oceans of North America, 75 million years ago.

The water was a clear, warm emerald, hazy with sunlight filtering down from the surface. You were hanging near the edge of the kelp beds, watching a small school of juvenile ammonites scatter, when the sunlight above was suddenly blocked. Not by a cloud, but by something far, far larger.

You turned just in time to see a massive shadow glide over you.

It was an Archelon. Even in a sea filled with terrifying monsters, this creature felt monumental. It was easily 15 feet from its sharp, curved beak to its blunt tail, and perhaps just as wide across its mighty, leathery flippers. It didn't swim so much as fly through the water, its huge, powerful front flippers beating with a slow, hypnotic rhythm.