You are in the forested plains of North America, 70 million years ago.

The air in the Cretaceous valley was thick, smelling of crushed ferns and something muskier. The quiet hum of insects was abruptly drowned out by a low, rhythmic thudding—the ground actually vibrated beneath your boots. You crouched behind the massive, fern-covered fallen log, your breath hitching in your throat.

They emerged from the treeline, not just a few, but dozens. Edmontosaurus. They were massive, easily thirty-five to forty feet long, with skin that looked like leathery mosaics of beige and greenish-brown, shifting in the dappled sunlight. Their heads, shaped like heavy boat hulls, swung slowly as they fed on the lush foliage. One of them, a monstrous adult, paused only fifty feet away. You could see the keratinous beak—dull, thick, and surprisingly intricate—stripping entire branches of conifers with a loud snap.

You watched a younger one, maybe only fifteen feet long, nudging its mother. The calf made a soft, clicking sound, totally different from the low-frequency booming rumble of the adults. Another large one lifted its body, momentarily walking on its powerful hind legs to reach higher into the canopy, its stiffened, tendon-reinforced tail balancing it perfectly. You didn't dare move. Even though they were herbivores, their sheer size was suffocating.