Millions of years ago, the megalodon shark was one of the scariest creatures to ever lurk in our seas. And even before that, the mosasaurs reigned supreme, terrorizing every ocean creature in sight.

Add Yahoo as a preferred source to see more of our stories on Google. Roaming the ancient seas eons ago, the megalodon shark eviscerated its prey with jaws that were 10 feet wide. Warpaintcobra/iStock ...