You are in the forested plains of North America, 110 million years ago.

The heat haze in the Arizona plains was distorting the horizon when you saw it—or rather, when you felt it. The ground trembled faintly, a rhythm that did not match the erratic gusts of wind.

Emerging from a stand of ancient, towering evergreens, the Sonorasaurus was immense. Standing at roughly 27 feet tall and nearly 50 feet long, it was a living hillside draped in a dappled, earthy grey hide that blended perfectly with the arid, rocky terrain. It moved with a slow, deliberate grace, its long neck swaying as it browsed on high branches.

As it passed, its massive, gracile limbs—similar to a brachiosaurid—thudded softly in the sandy soil. You were paralyzed in a hidden spot, barely breathing. Its eye, large and golden, seemed to look right through your hiding spot, displaying a tranquil indifference.