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Beneath the chilly and murky waters of the deep, swims one of the planet's oldest living species of predators; the shark; whose origins predate the dinosaur by 200 million years. Some scientists speculate that the very first ancestor of the shark was called Cretolamna, who was the ancestor of at least 3 branches of species of sharks. Some of these branches evolved into modern sharks, others simply disappeared. One of the species was the Megalodon (Carcharocles megalodon), which translates to "big toothed shark." Megalodon was most likely the largest predatory shark ever, with estimated measurements reaching up to 40 feet in length. Megalodon reigned the oceans during the Miocene era 18 million years ago, and vanished during the Pliocene era, 5 million years ago. Fossilized Megalodon teeth have been found around the world in Europe, Indonesia, Australia, New Zealand, Africa, and North and South America.

Sharks are at the top of the marine food chain and have no natural enemies. They play an important role in maintaining the marine ecosystem. If this is so, what then became of the Megalodon? Well for starters, the world the Megalodon entered had changed from the one it left. During the Miocene and Pliocene eras, a great continental change was underway. Continents were slowly shifting their way across the planet, transforming land and sea. During the Miocene period, the Indian subcontinent clashed into Asia, forming the Himalayas. Somewhere between 7 and 3 million years ago, the Isthmus of Panama emerged from the depths of the seafloor, joining North and South America and cutting off the last traces of the seaway that may have allowed the Megalodon to spread worldwide.

These effects also altered global patterns of wind and rain as the continents settled into their current positions. Then there was a widespread cooling which resulted in a glaciation period at the poles by the late Miocene period about 10 million years ago. In spite of the Megalodon's colossal size, it may have been unable to retain sufficient metabolic heat in cooler waters and this would have reduced the Megalodon's territory to the decreasing pools of warm coast waters. Scientist speculate that because of the Megalodon's inability to venture into the colder waters that were overflowing with an abundance of nourishment, the Megalodon may have starved to death.

Modern sharks have a modified circulatory system that allows them to preserve metabolic heat so that they can extend into chilly waters,with

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