Sharks are the great survivors, but the Meg is toast

Sharks have been a mainstay of the earth's marine population for half a billion years. (Tracey Nearmy/AAP PHOTOS)

Sharks adapted their skeletons, teeth and size to become the ultimate fighters of the sea world, surviving all five global mass extinction events over 500 million years.

But that doesn't mean there really is a megalodon lurking in the depths of the ocean, says John Long, a leading Australian palaeontologist and the author of a new book on sharks.