Unchanged for 200 million years because evolution couldn't improve the design, the saltwater crocodile is a 2,200-pound ambush predator with the strongest bite ever measured in the animal kingdom. Its death roll can dismember prey in seconds, and it can lurk motionless for hours before exploding from the water at terrifying speed. Dinosaurs went extinct; this thing didn't.

The largest land carnivore on Earth, the polar bear is a 1,500-pound Arctic killing machine perfectly engineered for sub-zero survival. Its paw swipe can decapitate a seal in one motion, and it can smell prey from 20 miles away across frozen tundra. Evolution looked at the grizzly bear and said 'what if we made it bigger, meaner, and gave it a fur coat rated to negative 50?'