Megalodon- A GIANT shark

It's not just the subject of bad sci-fi movies, this mega-shark prowled the deep 200 million years before dinosaurs even showed up.

This giant version of a great white shark first appeared over 400 million years ago during the Silurian Period, according to the San Diego Natural History Museum. They lurked in the warm water oceans preying on whales and other pinnipeds (carnivorious marine mammals). Yes, they ate whales. Scientists think they grew as long as 50 feet and weighed 50+ tons. To put that in perspective, the average weight of an orca whale is 7-8 tons; a Megalodon would be the combined weight of about 7 orcas! The longest known tooth was over 7 inches long.

They vanished about 200 million years ago, but we're still talking about them today. Some very entertaining takes on Megalodon include Nigel Marvin's sea monsters series where he goes back in time to swim with this giant and also the 2002 movie titled 'Megalodon' which is pretty ridiculous but is so bad that it's good.