You are in the forested plains of North America, 74 million years ago.

The air in the Montana basin was thick, hot, and smelled of crushed fern and humid earth—a stark contrast to the dustier, arid landscapes of the upland. You have been tracking the herd for days, finally catching up to them as they grazed through a lush, subtropical swamp. They were huge, nearly six meters long and weighing close to two tons, a sea of bony, hooked noses swaying through the dense vegetation.

As you moved closer, you can see the true scale of the Einiosaurus herd—it was a veritable sea of "buffalo lizards." Their most striking feature, the forward-curving nasal horn that looks for all the world like a prehistoric bottle opener, caught the golden afternoon light. They were moving as a single entity, the old males with their heavily damaged, heavily scarred, downward-hooking horns, asserting dominance with subtle head-tosses rather than direct conflict.