You are in the floodplains of South Africa, 255 million years ago.

The air in the late Permian swamp was thick enough to chew, smelling of sulfur and decaying giant ferns. You were crouching low, adjusting the focus on your camera, trying to capture the subtle color changes on a dragonfly the size of a seagull. That was when the sound stopped.

All the buzzing, croaking, and rustling in the undergrowth ceased instantly.

You froze, your breath catching in my throat. Fifty feet away, between two towering trees, the shadows seemed to shift and coalesce. A creature stepped out into a shaft of sunlight.

It was an Arctops.

It was not as large as a modern tiger, but far more unsettling. Its hide was mottled brown and red, thick and leathery, draped over a surprisingly fast, low-slung body. But it was the head that held you paralyzed—a flat, reptilian skull with the intelligent, predatory eyes of a mammal. And, of course, the teeth. Two massive, sabre-like fangs protruded from its upper jaw, curving down past its lower lip like ivory daggers.

It didn't roar. It didn't need to. It simply stopped, tilted its head, and focused on you with a calculating, hungry intensity. The creature took one step forward, its sharp claws gripping the damp moss, making no sound…