A strange cast of ferocious predators and giant herbivores lived here ... the ice age 20,000 years ago. In prehistoric North America, the short-faced bear (Arctodus simus) ruled the land.

Megatherium, the giant ground sloth ... and hyper-aggressive, this bear wouldn’t have hesitated to take on humans—or even other predators. Dunkleosteus was a prehistoric nightmare from ...

When global temperatures took a nosedive during the Pliocene epoch, this warm-water-loving giant ... prehistoric powerhouse made modern grizzlies look like teddy bears at a picnic. This ancient ...