What is the difference between the megalodon and the great white shark?

Great White Sharks are considered, by many ichthyiologists and paleontologist alike, to be more closely related to the mako shark than to the megalodon, as megalodon is often considered to be of the genus carcharocles as opposed to carcharodon, the genus of both the mako and the great white. They were originally considered to be members of the same genus secondary to similarities in their teeth, and both were thought to share a common ancestor, genus palaeocarcharodon. Many scientists now believe that the evolutionary paths of the two species were in fact divergent, the megalodon evolving from the Otodus obliquus, and the great white from the Isurus hastalis, or broad tooth mako.

In addition, megalodon was thought to grow anywhere from 43 ft. to 75 ft. long, and weigh approximately 47 metric tons to 70 metric tons. Comparatively, the typical great white shark is approximately 13-20 ft long with a weight range, note the use of kg as opposed to tons here, of 680-1900 kg. There have been reports of individual sharks, mainly unconfirmed, being up to 37 ft long. Most of these seem to have been reported earlier in the 20th century, and in some cases, estimates done from measurements based upon surviving photographs of these leviathans have shown that they were often much smaller than reported.

The most notable difference between the two species is, of course, the fact that the Great White has survived, and megalodon lost it's battle against extinction 1.5 million years ago during the pleistocene epoch. There are some notable differences in dentition and physiology as well, and wikipedia has articles on both species with a great attached bibliography for more information.

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