Megalodon

Megalodon is an extinct species of shark and was the largest of all time. Its scientific name is Otodus megalodon (meaning "big mouth"). It lived from the early Miocene to the Pliocene epochs, 23 to 3.6 million years ago (mya). It is not closely related to the present-day great white shark.
Megalodon had teeth, which are among the largest ever found, over long. Nicolaus Steno was the first to recognize the teeth as those of a giant shark. Paleontologists calculate that the shark was up to long with average length of 17 meters (56 feet) It weighed up to 48-103 metric tons.
Paleoecology
Fossil records of O. megalodon indicate that it occurred in deep to tropical latitudes. Before the formation of the Isthmus of Panama, the seas were relatively warmer. This would have made it possible for the species to live in all the oceans of the world.
O. megalodon lived in many marine environments (i.e. continental shelf waters, coastal upwelling, swampy coastal lagoons, sandy littorals, and offshore deep water environments), and moved from place to place. Adult O. megalodon were not abundant in shallow water environments, and mostly lurked offshore. C. megalodon may have moved between coastal and oceanic waters, at different stages in its life.
Its prey
Megalodon hunted large and medium-sized whales, attacking the bony areas, such as chest, fins, or tail. This would stop the whale, or it could kill quickly with a fatal bite to the chest region. The megalodon bite is considered one of the strongest bites in the animal kingdom's history.
Its great size, high-speed swimming capability, and powerful jaws coupled with formidable killing apparatus, made it an apex predator eating a range of fauna.
Fossil evidence is that C. megalodon preyed on cetaceans (i.e., dolphins, small whales, and Odobenocetops, and large whales, (including sperm whales, bowhead whales, and rorquals pinnipeds, porpoises, sirenians, and giant sea turtles.
Marine mammals were regular prey targets for megalodon. Many whale bones have been found with clear signs of large bite marks (deep gashes) made by teeth that match those of megalodon, and various excavations have revealed megalodon teeth lying close to the chewed remains of whales, and sometimes in direct association with them. Fossil evidence of interactions between megalodon and pinnipeds also exist. In one interesting observation, a megalodon tooth was found lying very close to a bitten earbone of a sea lion.
Relationships
Megalodon is now considered to be a member of the family Otodontidae, genus Otodus. Megalodon's older classification into Carcharodon was due to dental similarity with the great white shark. Most authors now think this is due to convergent evolution. The great white shark is more closely related to the extinct broad-toothed mako (Isurus hastalis) than to megalodon. The dentition in those two sharks is similar, whereas megalodon teeth have much finer serrations than great white shark teeth. The great white shark is more closely related to the mako shark (Isurus spp.), with a most recent common ancestor about 4 mya. Those who still think megalodon and the great white shark are more closely related, argue that the differences between their dentition are minute and obscure.