You are in the floodplains of North America, 152 million years ago

The air was still, heavy with the scent of pine and humid, rotting vegetation. Then came the sound-a low, rhythmic thudding that resonated in the chest cavity more than the ears. The ground began to vibrate-a deep, rhythmic thudding that shook the dew from the ferns.

You crouched behind a cycad, holding your breath as a massive form emerged from the mist. It was an Apatosaurus, its dark, striped hide camouflaged against the towering trees.

It didn't notice you. Its small head, situated at the end of a thirty-foot neck, casually sheared branches from the top of a tree with peg-like teeth. The sheer volume of foliage it consumed was staggering; this was an animal designed to eat constantly. Behind it, the rest of its herd trudge along in a long, slow file, dwarfing the surrounding foliage.