You are in the riverbanks of South America, 260 million years ago.

The air in the Permian basin was thick and humid, smelling of sulfur and decaying ferns. You were crouching near the edge of a shallow, murky river, taking soil samples, when the silence was broken—not by a roar, but by a sudden, heavy splash.

You looked up just in time to see a massive, squat shape erupt from the water-laden brush about thirty feet away. It was a Bageherpeton, a creature roughly the size of a modern alligator but far wider, with a skull flattened like a dinner plate and covered in rough, leathery skin. Its eyes, small and cold, were fixed directly on you.

It didn't hesitate. With surprising speed for its bulk, it charged forward on sprawling limbs, its enormous mouth opening to reveal rows of needle-like teeth…