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water, they had to compete with monsters like the 'sea scorpion', a giant euryptid, but they held their own and continued to thrive throughout the Devonian.

The beginning of the Carboniferous, with it's dropping sea levels, was so advantageous to sharks that the next 40 million years is often called 'The Golden Age of Sharks'. This is where the ancient shark afficionado really gets his kicks. This lot varied from most modern sharks in that their jaws were shorter and more rounded, not as strong, which suggests they weren't as fiercesome as they are today. But this was a time when life was a feast so our toothy friends were able to burst forth and multiply into an array of weird and wonderful forms. Here are some of the most jaw dropping:

-Stethocanthus grew to about 11ft long. Instead of a dorsal fin he had something which paleontologists believe resembled a brush. He also had an arrangement of teeth on the top of his head!

-Heliocanthus. We're not sure how big he was. When their fossil teeth were first discovered they were thought to be some kind of creature like an ammonite. The teeth are arranged in a characteristic whorl, which started under the jaw and spiralled outwards as the teeth aged.

-Falcatus. These were only 6 inches long. The males had a dorsal fin spine which grew into a long-forward growing appendage, thought to be relevant to courtship.

These are just the most popular, there were hundreds of weird variations, including giant sharks with 3 metre wide mouths.

As the Carboniferous matured, this explosion of diversity slowed and stagnated. For about 100 million years sharks stayed more or less the same. Having said that, this is the period when the first Xenocanths, eel-like sharks who lived in fresh water, came in to their own.
It was not until the next cataclysm (at the juncture of the Triassic and Jurrasic Periods) provoked the next great adaptive radiation that sharks began to take the forms we think of as modern sharks. Now, at last, we have arrived in the time of the dinosaurs. The early sharks shared the seas with ichthyosaurs and plesiaurs. The word cataclysm is closely related to the word catalyst, and this is how it has always been for sharks. The early Jurassic is also the time when the first rays, called guitar fishes, appeared. Another example was the Hybodus who lived between 165 and 150 million years ago. This specimen had two kinds of teeth for chomping on slippery food or for crunching the shells of sea urchins. He was about 6ft

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