The guys from Reactions have brought in best-selling author Sam Kean to debunk the Megalodon myth. The Megalodon, the 50-foot super shark is long-extinct. Period.
The Megalodons died 1.5 million years ago, but some teeth of these fish had a mysterious manganese layer on them, about 11 000 years worth. Evolutionarily, that is damn close to nowadays. That led some to believe that it still lives in the seas, but the truth is that the teeth had such a small layer of manganese because they were torn up from the old bedrock beneath the ocean floor.
Discovery Channel must bite its fingernails right now :))