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

The air in the Cretaceous marsh is dead silent. You’re trekking through a dense forest in what is now Montana, the damp earth clinging to your boots. Suddenly, you hear a sound—not a roar, but a dry, avian hiss, followed by a rustle in the ferns to your right.

You freeze. Emerging from the brush is a dinosaur about five feet tall and eleven feet long, sleek and covered in dark brown and gray feathers, resembling a flightless eagle—but far deadlier. It has sharp, forward-facing eyes, locked intently on you. As it moves, its feet make soft clicks on the rocky ground, keeping its massive, four-inch sickle-shaped claws lifted off the ground, held retracted and ready…