Super-fast giant prehistoric shark
Scientists say they've figured out how fast the megalodon - a giant prehistoric shark - used to swim, and it's way faster than any other shark species.
The megalodon, meaning "big tooth", is thought to have had a cruising speed of five metres a second - far faster than the cruising speed of some of the biggest sharks today.
The megalodon swam the world's oceans more than two and a half million years ago and was huge.
Scientists from the Zoological Society of London, who did the research, say it was at least 20 metres long - that's twice the length of a killer whale - and weighed 48,000kg - 48 times heavier than a great white shark!