Fish Age: (Devonian Period-370 million years ago)

The Devonian Period, or as we say, the Fish Age, was an era which saw great diversification in all fishes including Sharks. One of the earliest true fossils to be found intact was that of a Cladoselache (an ancient shark like fish). Intact fossils of ray fishes were found in the stomach of some of them, their orientation indicating that they were tail-first. So, we can say that Cladoselache was quiet capable of out-swimming its prey.

Cladoselache and other sharks living in those Devonian seas would have had to compete with the formidable armour-plated placoderm fishes. Yet, already the sharks had gained a tactical advantage with a body plan that was both simple and hydrodynamically efficient. With a pliable skeleton of cartilage that gave strength without weight, they were better adapted than their rivals and poised to go on to even greater things.

These fossil teeth of an ancient sand tiger shark Odontaspis robusta were found in Kent, England. Their owner lived in the early Eocene epoch, about 50 million years ago. The slender teeth are from the front of the mouth and the broader-based ones are from the side.