For 65 million years, fantastic creatures roamed the Earth, but they disappeared at the end of the last Ice Age. Learn what caused their demise.
The mega beast Megalania -- an 18-foot lizard with a mouthful of dagger teeth and venom -- was the biggest reptilian predator since T-Rex.
Acrocanthosaurus, which lived 50 million years before T-Rex, had the most powerful arms of all dinosaurs, a scissorlike bite and a hi-tech neck brace.
Meet Spinosaurus -- king of dinosaurs 100 million years ago -- a carnivore twice the size of T-Rex with a long crocodilian skull and massive claws.
With six-foot jaws and a nasty disposition, the Mosasaur had an extra set of teeth on the roof of its mouth and dined on giant sharks and Plesiosaurs.
Terror Bird bashed its victims' brains in with its beak and swallowed giant rodents. It dominated a continent, battling wolves and saber tooth cats.
Long-extinct giant beasts and the strange world they once inhabited areresurrected through fossil evidence and other scientific data in this Discovery Channel program that reveals how these creatures once lived and flourished.