You are in the floodplains of North America, 108 million years ago.

The air in the Early Cretaceous floodplain was thick, humid, and smelled of wet earth and cycads. You crouched behind a dense fern thicket, watching a 20-foot-long Sauropelta move slowly toward the riverbank, its armored skin dappled with sunlight filtering through the canopy.

It was a fortress on four legs, a low-slung, 2-ton nodosaurid covered in bony plates that ran down its back. Its neck was almost entirely hidden by massive, projecting shoulder spines that seemed designed specifically to deter large carnivores. It moved with a slow, grinding patience, focused entirely on tearing low-lying foliage with its strong beak.

As it approached the water, the beast paused, turning its head slowly to look in your direction. There was no fear in its gaze, only a calm, heavy awareness. Even though it lacked the tail club of later ankylosaurs, the sheer bulk of its armored tail and the vicious spikes along its flanks made it clear that this animal was a walking tank.