You are in the forests of South America, 2 million years ago.

The air in the subtropical forest was thick and humid, filled with the scent of pine resin and wet ferns. You were moving cautiously, following a faint game trail, when the silence became absolute. The chatter of small birds ceased.

Following the faint odor of carrion, you stepped over a large root and froze. Several yards away from where you stood was a bear.

It was sleeping, yet it did not look like a typical bear. It was vast, its coat a thick, coarse brown, looking more like a mountain of fur than a living creature. It must have weighed more than a ton, its massive legs tucked under a body roughly the size of a small rhinoceros. It was resting in a sunny clearing among tall ferns—its territory that you have stumbled upon.

The creature’s short, deep snout—the hallmark of its kind—rested on its paws. Its heavy ribs rose and fell in slow, rhythmic breaths.

As you shifted to avoid the sleeping bear, a twig snapped under your boot.

The beast didn't wake frantically. It simply ceased to be asleep. One minute it was in a deep slumber, the next, a single, incredibly heavy eyelid opened, revealing a dark, calculating eye. It didn't rise immediately. It merely turned its massive head, focusing on you with a disinterest that turned to intense focus in a heartbeat…