You are in the coastal forests of North America, 75 million years ago.

The scent of damp fern and sulfur hit you first, heavy in the humid air of the Late Cretaceous. You froze behind a thick fern frond, heart hammered against your ribs, as the 30-foot-long tyrannosaur burst from the treeline of the swamp.

It wasn't a T. rex for sure, but nonetheless dangerous. It was more slender, but its deep, hooked snout was terrifyingly close to your hiding spot, searching for prey. The facial, scaly scutes twitched as the tyrannosaur analyzed the air. Its binocular vision—far superior to most other predators—focused on the marsh in front of you.

As it moved, its long legs carried it with startling speed. The tyrannosaur stopped, lifting one foot, and for a split second, its intense eyes met mine. Its jaws slightly opened, revealing the specialized, sharp teeth of a basal tyrannosaurid, designed for crushing and tearing…