The Megalodon was the biggest shark that ever lived, but people still wonder if it could be hiding out in the depths of the ocean somewhere. Even though the ocean covers 70% of Earth's surface and is still largely unexplored, the Megalodon went extinct about 3 million years ago, as that's when it disappeared from the fossil record. Megalodons preferred swimming in warmer waters and required lots of large prey to feed on, so it's theorized that when the climate cooled, they lost habitat and signi