You are in the floodplains of Mongolia, Asia, 70 million years ago.

The air in the Cretaceous forest was thick and humid. You were crouched behind a large fern, scanning the forest floor for fossils, when you heard a soft thud-thud-thud.

Bursting through the foliage, a Homalocephale appeared. It was small, maybe only six feet from its beak to the end of its stiff tail. Unlike the domed skulls of its relatives, this dinosaur had a strikingly flat, wedge-shaped head.

It was browsing on low shrubs, its rounded eyes taking in its surroundings. Suddenly, it froze, sensing your presence. Instead of fleeing, it tilted its flat, thick skull, gazing at you with curiosity. It gave a playful, low grumble, almost as if inviting you to play, and knocked its head gently against a fallen log—a behavior that scientists suggest they used for friendly, non-lethal head-butting.