This short-faced bear was twice the size of a grizzly and could outrun a horse. It roamed North America for a million years, then went extinct. See how this mighty creature lived, hunted and vanished.

Megalodon. It was the biggest predator to ever swim the oceans of the world. For 20 million years, this ferocious 50-ton shark with a 7-foot jaw and seven inch teeth terrorized the creatures of the seas from Australia to South America and the coasts of North America. Not even the giant whales of the time were safe from this apex predator. Now, nearly 2 million years after Megalodon disappeared from earth, scientists will rebuild this monster shark.

The Sabertooth dominated the primal landscape of the Americas for nearly two million years, then suddenly, mysteriously went extinct. Find out how it lived, how it killed, and how it died.

The dire wolf, a fierce and powerful alpha predator in the savage ice age, was larger and more powerful than any modern-day wolf. Why did it suddenly perish while the smaller, weaker gray wolf survived?

The Terror Birds of South America may be the most unusual predators ever to roam the face of the Earth. Until about five million years ago, the continent of South America was totally isolated by water from the rest of the world. A water gap separated the South from North America, and as a result, evolution had a chance to experiment. After the dinosaurs died out 65 million years ago, they left an ecological gap. The role of top predators in their world was left empty when they were no longer around. In the rest of the world, mammals filled in that gap the creatures that would evolve into sabre tooth cats, wolves and bears. But in South America, large, flightless birds evolved into the Top Predator role. These were the Terror Birds the only birds ever to become Top Predators on an entire continent.

At four feet wide and 1,000 pounds, the killer pig was a prehistoric battle tank that dominated the North American landscape. Endowed with some truly unique bioengineering traits, the killer pig relied on its massive three-foot-long skull and binocular vision to catch its prey. Learn how the killer pig was an evolutionary success, despite its eventual extinction.

Hyaenodon created a reign of terror by just using its head. It dominated with this one lethal weapon that could dispatch a prey animal within seconds. This beast is a perfect example of an animal rising far above its potential. Its powerful, razor sharp bite left a mark in history that will never be matched.