This shark devours a sea lion before being chased in turn

Thanks to unearthed fossilized teeth and scales, sharks are estimated to have existed for over 400 million years, long before the dinosaurs. The ocean’s top predators have evolved into some 500 species of all sizes and colors, with varying diets and behavior.

Like rays, sharks belong to a subclass of fish called elasmobranchii. Species in this subclass have a skeleton made of cartilage, not bone, and have five to seven gill slits on each side of the head (most other fish have only one gill slit on each side ), which they use to filter oxygen from the water.

Tremendous predators, sharks have mouths lined with multiple rows of individual teeth that regularly shed and regrow. Their teeth come in all shapes and sizes, from razor-serrated to triangular like a spear – as seen in the video above.

Sharks are found in deep and shallow waters throughout the world’s oceans, with some migrating great distances to breed and feed. Some species are solitary, while others live in groups to varying degrees. Lemon sharks, for example, have been found to gather in groups to socialize.

Most sharks feed on small fish and invertebrates, but some of the larger species feed on seals, sea lions – as in the video above – and other marine mammals.

Sharks may not be a significant threat to humans, but we are one of the main threats to this category of marine animals. Overfishing is the biggest threat. An estimated 100 million sharks are killed each year, mostly to meet demand for an expensive Chinese dish, shark fin soup. Sometimes fishermen cut off the fins of live sharks and throw the finless animals back into the ocean, where they drown or bleed to death. This practice, called shark finningis used to save space on the boat (the fins are the most valuable part of the shark) and to avoid exceeding fishing quotas.

Rising water temperatures and coastal development are also contributing to declining populations by destroying mangroves and coral reefs that sharks use to breed, hunt and protect young. As the ocean’s top predators, sharks play a vital role in balancing the food web.

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