A prehistoric monster shark that first appeared about 20 million years ago, megalodon (Carcharodon megalodon) is the largest meat-eating fish that ever lived. In the 1600s, the physician Nicholas Steno realized that the mysterious "tongue stones" that people had thought belonged to snakes or dragons actually resembled shark teeth. Since then, by observing modern sharks and examining fossilized megalodon parts, scientists have concluded many interesting facts about its size, habitat and diet, and the reasons it became extinct.
Scientists have estimated megalodon's size from fossils of its teeth and spine. Shark skeletons are made of cartilage, which breaks down quickly after death and only rarely survives as fossils, but many hundreds of fossil megalodon teeth have been found, as well as boney segments of its spine, called centra. By comparing these with modern sharks, scientists estimate megalodon grew about 14 to 18 meters (45 to 60 feet) long, or about the same size as a bus, and weighed 50 to 77 tons. It had 46 front-row teeth, and because most sharks have six rows of teeth, scientists think it had about 276 teeth altogether in a mouth over 2 meters (about 7 feet) wide.
Megalodon swam in the warm oceans of prehistoric Earth. Fossils of megalodon have been found in many places around the world, including the United States, Japan, Europe, Australia and Africa, and scientists have concluded it swam in warm intercontinental oceans. If megalodon's habitat was the same as that of today's great white shark's, it lived in deep water offshore and traveled to warmer, more shallow waters to breed. In 2009, scientists discovered a megalodon nursery in Panama that contained fossilized teeth of juvenile megalodon. This evidence, together with earlier evidence of a breeding ground in South Carolina, led them to estimate a juvenile megalodon was about 20 feet long, or the size of a great white shark.
Whales, seals, sea lions, walruses and other large marine mammals and fish were part of megalodon's diet. Whale bone fossils showing serrated bite marks that fit megalodon teeth show that whales were a megalodon prey animal. Its jaws were so strong it could crush a whale skull as easily as you can eat a piece of fruit. Like large modern sharks, megalodon probably also ate other marine mammals and fish, surprising them by swimming quickly upward from deep water. Scientists think megalodon ate more than 1,100 kilograms (about 2,500 pounds) of food a day.
Megalodon became extinct about 2 million years ago. Some scientists think falling ocean temperatures in the last ice age allowed whales, its main food source, to migrate to colder areas where megalodon couldn't follow. They also suggest that great white sharks, orcas and other predators killed so many juvenile megalodon that eventually it died out. Other scientists think the oceans became too cold for megalodon to survive. Although megalodon probably looked like a great white shark, scientists still don't know whether the two animals are directly related or if megalodon had no direct relations and was an evolutionary dead end.