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long and looked like a typical shark.

There were 3 more of these extinction events, punctuating the Triassic and Jurassic periods. Sharks survived. Even when the dinosaurs, along with 70% of the Earth's population, were wiped out 64 million years ago at the end of the Cretacous Period, sharks survived.

We are rapidly approaching the present day and the sharks have gotten very familiar:

'Oceans in the Cretaceous period (140 to 65 million years ago) were dominated by goblin, sand, probable, nurse, cow and angel sharks.' (Reefquest)

By the early Eocene, 50 million years ago, we also find fossil records of sand tiger sharks (Ondontaspis robusta) and the first 'ground sharks', the Carcharinids developing alongside the first whales. These are the forerunners of blue sharks and cat sharks.

Everybody's favourite shark, the Great White, is now thought to have evolved from Isurus hastalis, a Maku shark whose teeth resembled a Great White's and lived about 65 million years ago. Previously the Megalodon was the prime candidate. Megalodon was descended from a mackerel shark who lived between 60 and 45 million years ago. It reached its maximum size about 12 million years ago. At about 50ft in length, with 6" teeth, he could almost have swallowed our Great White whole.

By the time we reach the Miocene Period the direct ancestors of all the sharks we know today had made their appearance.

The story of the shark is also a story about the changing tides of geological time. The basic structure of a shark is one of nature's most successful, adapting and ultimately profiting by the most destructive events since time began.

If you would like to find out more about sharks and their ancestors, here are some good places to look at:

BBC Walking with Dinosaurs web-site
New Scientist
National Geographic
'Prehistoric Sharks' by Duncan Graham-Rowe
ReefQuest Centre for Shark Research

Learn more about this author, Briar Shaw.
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