Megalodon prehistoric shark, artwork, chasing a school of fish. Megalodon, Carcharocles (Carcharodon) megalodon, was an enormous shark that lived between around 20 and 1.2 million years ago, and is known only from fossils. It was related to the modern great white shark, and is thought to have fed on whales, as this is the only source of food that could have provided it with enough meat. Megalodon was thought to attain lengths exceeding 20 metres, and possibly significantly larger. It is thought that it died out after the seas cooled, allowing warm-blooded whales to escape the sharks for much of the year by swimming to waters too cold for them to survive in.