Sharks have patrolled the world's oceans for hundreds of millions of years, yet pop culture still paints them as mindless killing machines. In reality, sharks are a wildly diverse group of animals with extraordinary senses and a critical role in keeping marine ecosystems in balance.
Here are verified facts about sharks that go beyond the movie myths.
There are more than 500 known species of sharks, ranging from the dwarf lantern shark, which is small enough to fit in a human hand at about 8 inches long, to the whale shark, the largest fish in the world.
Whale sharks typically grow 18 to 32 feet long, though individuals as long as 40 feet have been documented.
Sharks first appeared in the fossil record more than 400 million years ago, predating dinosaurs by roughly 200 million years.
Sharks detect electrical fields given off by other animals using organs called the ampullae of Lorenzini, tiny jelly-filled pores clustered around their snouts.
Shark skin is covered in tooth-like scales called dermal denticles, which reduce drag and turbulence and help sharks swim more efficiently.
Many shark species continuously shed and regrow teeth throughout their lives, and some can go through tens of thousands of teeth in a lifetime.
Sharks have skeletons made of cartilage rather than bone, which makes them lighter and more flexible in the water.
Only a small number of shark species, such as the great white, tiger, and bull shark, are involved in the majority of recorded shark bites on humans.
As apex or near-apex predators, sharks help regulate the populations of the species below them in the food web, which keeps marine ecosystems balanced.
Shark finning, the practice of removing a shark's fins (often for shark fin soup) and discarding the rest of the animal, has driven steep population declines in several shark species.
Humans kill far more sharks each year than sharks kill humans; overfishing, bycatch, and habitat loss are the biggest threats sharks face.
Sharks must keep water moving over their gills to extract oxygen; some species can pump water over their gills while resting, while others must swim continuously.
Many sharks have a reflective layer behind the retina called the tapetum lucidum, which improves their vision in low light.
Sharks are found in every ocean on Earth, and some species, like the bull shark, can also tolerate freshwater rivers and lakes.
The Greenland shark is one of the longest-living vertebrates known, with scientific estimates suggesting a lifespan that can exceed 250 years.
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