

Sharks are amazing fish that have been around since long before the dinosaurs existed. They live in waters all over the world, in every ocean, and even in some rivers and lakes.
Unlike bony fish, sharks have no bones; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. Sharks also have no swim bladder (unlike bony fish)
andMany paleontologists are very interested in living groups, because the study of the living organisms can both unlock their evolutionary history and provide important keys towards interpreting their fossil record. Some living groups have ancient histories. For example, sharks have existed as a group for over 350 million years! Today, sharks and rays (elasmobranchs) are represented by over 600 species that show a remarkable range of ecological and morphological diversity. Unlike the true fishes, sharks do not have internal bone, but instead have a cartilaginous skeleton. Although many people are told that sharks are primitive in comparison to other groups, this is not true. Many sharks are efficient and specialized hunters that have thrived for millions of years.