Shark

Sharks star in blockbuster movies as blood-seeking villains, but in reality they’re far more fascinating and complicated than they’re often depicted in pop culture.

Based on fossilized teeth and scales, scientists believe that sharks have been around for more than 400 million years—long before the dinosaurs. The ocean’s top predators have evolved into roughly 500 species that come in all different sizes and colors and have varying diets and behavior.

Anatomy

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

Whale sharks, the largest fish species on Earth, can grow to more than 55 feet, while dwarf lantern sharks reach a mere eight inches.

Formidable predators, sharks have mouths lined with multiple rows of individual teeth that fall out and grow back on a routine basis. Their teeth come in all sizes and shapes, from serrated like a razor to triangular like a spear.