For the next 13 million years the enormous shark dominated the oceans until becoming extinct just 3.6 million years ago. O. megalodon was not only the biggest shark in the world, but one of the largest fish ever to exist. ... In fact, the word megalodon simply means 'large tooth'.

How do they know megalodon existed?

We know primarily about Megalodon's existence through fossilized teeth. Megalodon's maximum size is inferred because we do not actually have a whole preserved Megalodon. Using a mathematical relationship between body size and tooth size for Great Whites, we can estimate Megalodon's size from its teeth.

Why do Megalodons not exist?

Megalodon evolved into a deep sea predator and is still roaming the deep seas. There is no scientific evidence of megalodon evolving into anything else. Evidence suggests it went extinct approximately 3.5 million years ago with many of the large marine animals during the mid-end Pliocene.