Sharks appear for the first time in the fossil record 455 million years ago. However, they did not become common until the Devonian, some 400 million years ago. To study the evolution of these marine animals is not easy, given that they have cartilage skeletons that do not completely fossilize. Fortunately, fossilized denticles, teeth and vertebrae have been found, which allow us to know sharks’ origin. The oldest shark is the Antarctilmna. This species probably lived in freshwater areas about 380 million years ago.