The megalodon, a prehistoric ancestor of the modern shark, appeared about 18 million years ago and became extinct 2 million years ago. Like today's great white shark, it had 5 rows of 46 teeth for a total of 320. However, the teeth were much larger, fitting in a jaw 10 feet across and 8 feet high. The megalodon was about 60 feet long, nearly 3 times the length of the great white shark. Cast from a tooth in the Babiarz Institute of Paleontological Studies archives.