You are in the forests of North America, 49 million years ago.

The air was thick and humid, echoing with the calls of early mammals you couldn't identify. You were navigating the dense, subtropical forest. The sun barely pierced the canopy, creating a, shimmering haze above the damp, fern-covered ground. Suddenly, a massive, muscular figure stepped from behind a cluster of giant ferns. It was over 6 feet tall, clad in thick, brown-greenish, fur-like feathers.

You froze upon recognizing it. It was a Gastornis. Its massive head, easily the size of a horse’s, turned slowly toward you. It didn't look like the vicious, razor-hooked "terror birds" you had imagined. Its beak was immense—a yellow, deep, and broad, lacking a sharp hook but looking fully capable of crushing a small tree, let alone a human. The animal made a low, guttural croak, staring with small, intense eyes, causing you to take a step back.

Is it a predator? Or something else? Those were the mind-blogging questions you wonder as you are confronted by the big bird…