Megalodon is a massive prehistoric shark, that evolved in the Oligocene Epoch 25 Million Years Ago, and only went extinct around 1.5 Million Years Ago or less. Their extinction was caused by Ice Age climate changes around 2 million years ago, which made the baleen whales that were the bulk and mainstay of the diet of Megalodon, to move from the warm water tropics to the freezing polar waters (as in turn the whales nutrition moved South also) They likely lasted to just over if not a little lesson than 1 Million Years BCE. As Megalodon was restricted to warmer waters around the tropics, with its blood type, it could never follow its prey. It is likely the last of the Megalodon starved to death. They were a gigantic horror of the depths, at 18-21 metres long. The full name of Megalodon is Carcharodon megalodon (although some think it is not closely related to the great white shark and place it in a new genus, Carcharocles).
Walking with Dinosaurs
Megalodon doesn't feature in the main series.
Megalodon features in Sea Monsters: A Walking with Dinosaurs Trilogy, and belongs to the third most dangerous sea of all time. Because they are so dangerous, Nigel Marven's team didn't want him to swim with them, so they decided that he had to swim with the juveniles first. The juveniles alone were the size of Great White Sharks. The juveniles hunt the bizarre Odobenocetops.