The prehistoric seas were once haunted by supergiant predators, the Megalodon sharks. With a lenght of about 60-100 feet, this monstruous predator is said to be still alive today. In fact, the Megalodon and the Great White Shark are very similar, beside of the size (it's lenght is only 10 to 20 feet). The only proof of Megalodon's existance is a huge jaw, because the rest of the body, made up with cartilage, which is not saved in sediments.
But how about the possibility of having some still alive today? In 1918, two fishermen, while looking for crayfish in Port Stephens, Australia, reported seeing a monstruous white shark that was at least 100 feet long. (One said it was three hundred feet long, the other said it was more like one hundred.) However, this is usually believed to be just another exaggerated "fish story", what I also think personally. For example, the color of the animal, a bright white color, would be extremely unusual for any marine animal. Even the great white shark is only white on its stomach. A huge albino shark such as this one would have nature against it -- its color would be easy to spot by prey and it probably wouldn't be able to survive.
Zane Grey, author and deep-sea fisherman, also reported seeing a huge shark in the South Pacific (off Rangiroa) in about 1927. He described the shark as being 35 or 40 feet long, which is not unusually large. He also said that it had a greenish-yellow color, with some white spots. The key of the sight: all details tend to say that Grey saw a Whale Shark, (Rhincodon typus), a shark that reaches lengths of 50 feet, and is a gentle giant, plancton eater, that is sometime possible to take a ride on. Grey, however, did not believe that what he saw was a whale shark. This also can be a very large tiger shark (Galeocerdo cuvier). Tiger sharks are much more fearsome than whale sharks, and also live in deeper waters.
About six years later, Grey's son Loren claimed to see a megalodon himself. He was also convinced that what he saw what not a whale shark (or a true whale). While on board the S.S. Manganui, Loren saw a barnacle-covered, yellowish creature with a huge brown tail and a round head that was 10 to 12 feet long. The entire animal, which he thought was without doubt a shark, was 40 to 50 feet in length. However, whatever kind of shark it was, it wasn't any form of a white shark. The coloring, particularly the brown tail, does not match the physiology of the white shark. I think it can be a Bigmouth shark (I forgot the latin name, sorry), that have the same color and similar size.
There are other sightings, but I don't give them. This is inutile: the way it goes is that Megalodon is really extinct and Whale Shark is often mistaken for an animal more dangerous than it.
SOURCES: http://www.crosswinds.net/~mothman/megalodon.htm
Cryptozoologix 2001
