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

The sun was high over the Western Interior Seaway in the late Cretaceous, but the deep water below your small, crude raft was a dark, inviting blue. You were scanning the surface, taking a breath of calm, when the water began to ripple unnaturally.

It happened in seconds.

Without warning, a massive dark shadow emerged from the abyss directly beneath you. It was a Tylosaurus. As long as a small whale, the mosasaur’s muscular body powered it upward at terrifying speed, aiming to shatter whatever was above it.