Megalodon

It was once believed that the Megalodon ("Meg") was the ancestor of the modern Great White Shark (some still do). I am among the growing many, who believe that Meg is a cousin. These cousins were actually in competition with each other for supremacy in the ancient oceans. Meg was much larger, and likely fed primarily on sea lion, whale and giant squid. The real competition was between juvenile Meg and Great White, both of whom would likely have fed on smaller prey.

One thing that may have doomed Meg, was the Great White's speed and it's more efficient teeth (thinner and more coarsely serrated). At the same time, whales (Meg's primary prey) were developing muscle and tail structure that allowed them to swim faster. For these two reasons, and probably others, it is believed that Meg is now extinct. At least, most people think so. If they still existed, they would live in the deep ocean and might go unseen, or be mistaken for a whale. Stories of giant sharks have been passed down for centuries and there have even been 20th century sightings. These sightings though, are always explained away by skeptics. They say that the experienced seamen are telling "fish stories," or are fooled by a case of mistaken identity - but who knows? If the Megalodon does still exist, it would be larger than the exaggerated shark in the film "Jaws".