Carcharocles megalodon, sometimes called Carcharodon megalodon, was a giant shark similar to, but much larger than, the modern great white shark Carcharodon carcharias. Megalodon may have been the largest predator ever to have lived. The maximum size reached by Megalodon is still debated, but a length of 15 to 20 meters is widely accepted. This means megalodon was at least three times larger than the great white.
Megalodon probably became extinct around the end of the Pliocene about two million years ago. Some believe megalodon is not yet extinct and point to finds of teeth with ages around 11,000 to 24,000 years as well as sightings of large sharks by fishermen. For example, in 1918 lobster fishermen from New Zealand reported spotting a shark whose length they estimated exceeded 30 meters. However, like the great white shark of today, megalodon probably lived in shallow coastal waters. It should have been spotted often if it still existed. See Ben S. Roesch's article which argues against the survival of the megalodon to the present.
The whale shark Rhincodon typus (right) may explain some "megalodon" reports. The whale shark is the largest known fish. It reaches a length of 15m and a weight of 18 metric tons. The top of the whale shark is colored a deep blue while its underside is white. White spots and vertical lines mark its body. The whale shark feeds on small fish and plankton. It is considered harmless to humans. Encounters with a "megalodon" described as covered in white spots probably originate with sightings of the whale shark.