Ocean Life - Sharks: ancient ocean predators with cartilage skeletons

Sharks are cartilaginous fish defined by ribless skeletons, replaceable teeth, and five to seven gill slits. Fossilized shark-like scales date back more than four hundred million years, while modern sharks emerged around two hundred million years ago. Their sizes span from the tiny seventeen-centimeter dwarf lanternshark to the massive whale shark, the world's largest fish. Although several species serve as apex predators, overfishing and practices such as shark finning have driven a seventy-one percent decline in global shark populations since nineteen-seventy.

Source: Wikipedia