You are in the coal forests of North America, 302 million years ago.

The air in the Carboniferous forest was thick, hot, and smelled intensely of damp earth and rotting vegetation. You stepped carefully over a log, while watching the humid haze. That’s when you saw it—a flash of movement near a second fallen log.

It was a Petrolacosaurus, small, perhaps only 40 centimeters long, yet it moved with an unnatural, jarring speed that made it seem larger. Its skin looked like polished dark green leather, catching the dappled light filtering through the canopy, perfectly adapted to this dry, inland climate. It stopped, lifting its slender, lizard-like head. Its large, dark eyes seemed to look right through you, looking for bugs rather than a human observer.

You held your breath as it darted forward, chasing a prehistoric insect, its muscles moving smoothly. This wasn't a slow, lumbering amphibian; this was something faster, more efficient—an early diapsid. For a few seconds, it stood still, its tiny, complex heart powering it through the humid heat, a fast-pumping engine that signaled the future of life on land.