Sharks have lived in the ocean for over 400 million years, making them older than trees and dinosaurs.

The oldest shark-like fossils are scales found in Siberia and Australia. These fossils date back about 420 to 450 million years. The first trees did not appear until about 350 to 370 million years ago. This means sharks were swimming in the ocean for at least 50 million years before the first forests existed.Sharks are different from most fish because their skeletons are made of cartilage. Cartilage is the same flexible material found in human ears and noses. While cartilage does not turn into fossils easily, shark teeth are very hard. A single shark can grow and lose 35,000 teeth in its life. These teeth provide a clear record of shark history for scientists.Sharks also lived 200 million years before the first dinosaurs. Dinosaurs appeared about 230 million years ago, but sharks were already top hunters by then. They survived the Permian-Triassic extinction 252 million years ago. This event killed 96% of all life in the ocean, but sharks lived through it.Sharks have special senses that help them survive. They can feel electricity from other animals using a sense called electroreception. They also have very strong immune systems. Today, there are more than 500 different species of sharks living in every part of the ocean.