Sharks

Older Than Trees

Picture the Earth 450 million years ago. There are no trees, no flowers, no insects and no animals with legs. The land is bare rock and moss. But in the sea, something with a long body, a strong tail and skin like sandpaper is already hunting. That is the start of the shark story, and it has not stopped since.

Sharks are older than trees. The first trees did not appear until about 385 million years ago, some 65 million years after the first shark scales. Sharks are older than dinosaurs by 200 million years. They were swimming before Mount Everest existed and before the Atlantic Ocean opened. In all that time the oceans have been hit by five mass extinctions, the kind of disaster that wiped out the dinosaurs. Sharks came through every one that struck after they appeared, which by the count of London's Natural History Museum is all five.

Today more than 500 species share the name. Some are smaller than a pencil. One is the largest fish on the planet. Some live in rivers, some inside an erupting volcano, some in water so deep and cold that their hearts beat six times a minute. One kind lives for 400 years. This page is about all of them.

Sharks have survived all five of Earth's mass extinctions. The one they may not survive is made of nets and hooks.

What Is a Shark?

A shark is a fish. That surprises some people, because sharks do not look much like goldfish or tuna. But a shark lives in water, breathes through gills and is cold-blooded. It is a fish of a special kind: a cartilaginous fish, which means its skeleton is made of cartilage instead of bone.

Cartilage is the flexible, rubbery stuff in the tip of your nose and the edge of your ear. It is lighter than bone and bends without breaking. Bony fish, which are most of the fish you know, have hard bone skeletons. Sharks, rays, skates and a strange group called chimaeras have cartilage. Together they form the class Chondrichthyes (kon-DRIK-thee-eez), a Greek word meaning "cartilage fish."

What makes a shark a shark

Scientists sort sharks out from their cousins by a short checklist. A shark has:

• A skeleton of cartilage, hardened with minerals only where it needs strength, in the jaws and the backbone.
• Five to seven pairs of gill slits on the sides of its head, open to the water. Bony fish hide their gills under a flap.
• Skin made of tiny teeth. Every scale is a miniature tooth called a dermal denticle.
• Teeth that are never finished. Rows of new teeth wait behind the old ones for life.
• No swim bladder. Bony fish float with a gas-filled bag. Sharks use an oily liver and keep swimming.

Rays and skates have the same cartilage skeleton and the same tooth-like skin. But their gill slits are on their undersides, and their bodies are flat, with the fins spread out like wings. A ray is a shark's closest cousin, not a shark. Chimaeras, also called ghost sharks, split off even earlier and have a single gill opening on each side. Dolphins, which are often mistaken for sharks at the beach, are not fish at all. They are mammals that breathe air and nurse their young.

Built to Hunt

Everything about a shark's body is tuned for moving through water and catching food in it. Four hundred million years of trial and error have produced a design that engineers now copy for swimsuits, airplane wings and wind turbines.

Skin made of teeth

Run your hand along a shark from head to tail and it feels smooth. Run it the other way and it feels like sandpaper. That is because shark skin is covered with millions of tiny tooth-like scales called dermal denticles. Each one has an enamel-like coat, a layer of dentine and a pulp cavity inside, exactly like a tooth. The denticles have tiny ridges that break up the water flowing over the shark, so it slips along with less drag. For centuries people dried shark skin into a natural sandpaper called shagreen and used it to smooth wood. In 2018 engineers who molded mako denticles onto an airplane wing section found the pattern cut drag and added lift at the same time.

A conveyor belt of teeth

A shark's teeth are not rooted in its jaw the way yours are. They sit in the gums in rows, like a conveyor belt. When a front tooth breaks or falls out, the tooth behind it moves forward to take its place, in some species within a week. A shark may have several hundred teeth in its mouth at once. Over a lifetime it goes through tens of thousands; estimates for a great white run from 20,000 to 35,000. That is why fossil shark teeth are the most common vertebrate fossils on Earth.

Different sharks have very different teeth. A great white's are broad triangles with saw edges for cutting through seals. A mako's are long spikes for grabbing slippery fish. A Port Jackson shark has pointed teeth in front and flat molars in back for crushing sea urchins. Its scientific name, Heterodontus, means "different teeth." A whale shark has about 300 rows of tiny teeth that it does not use at all.

A jaw that reaches out

Your upper jaw is part of your skull. A shark's is not. Its jaws hang in slings of muscle and ligament below the skull, so the whole mouth can push forward to grab prey. That is why slow-motion film of a great white looks as if the mouth launches ahead of the head. The deep-sea goblin shark takes this to the extreme. It shoots its jaws out from under its blade-like snout farther and faster than any other shark measured, a trick researchers filmed in 2016 and named "slingshot feeding."

The oily liver

Bony fish stay afloat with a swim bladder, a gas-filled bag inside the body. Sharks have none. Instead they carry an enormous liver full of an oil called squalene, which is lighter than water. In some species the liver is a quarter of the shark's whole weight. The oil helps, but it is not enough on its own, so most sharks also get lift from their wing-shaped pectoral fins and their tails as they swim. A shark that stops moving slowly sinks.

Breathing on the move

Sharks breathe by passing water over their gills, where oxygen moves into the blood. There are two ways to do it. Some sharks pump water over the gills with their cheek muscles, which lets them rest on the bottom. Nurse sharks sleep this way in piles. Other sharks, called ram ventilators, breathe only by swimming forward with their mouths open. Great whites, makos and whale sharks are built this way. If one stops swimming for long, it suffocates. That is the grain of truth behind the old saying that sharks must swim or die. It is true for a minority of species, the great white, the makos, the whale shark and the blue and bull sharks among them, and false for most of the rest.

Warm-blooded sharks

Most sharks are as cold as the water around them. The mackerel sharks are different. Great whites, makos, porbeagles and salmon sharks have bundles of blood vessels that trap heat from their muscles, keeping their swimming muscles, eyes and brain warmer than the sea. A salmon shark in the icy North Pacific keeps its body near 25 °C (77 °F). A warm eye sees fast prey in cold water, and a warm muscle fires faster. The great white hunts pre-heated.

Super Senses

You have five senses. A shark has at least seven, and several of its five are sharper than yours. A shark hunting in murky water is reading smells, sounds, pressure waves, electric fields and the Earth's magnetic field all at once.

Smell in stereo

A shark's nostrils are not for breathing. They are pure smell organs, and they work in stereo. In a 2010 experiment, scientists fitted small sharks with headgear that fed squid scent to each nostril separately. The sharks turned toward whichever nostril caught the smell first, even when the other nostril got a stronger dose, on time gaps as short as a tenth of a second. Smell in the sea arrives in ragged patches, so timing beats strength for tracking a scent back to its source. The great white gives about 18 percent of its brain to smell, more than any other shark.

The electric sense

Look closely at a shark's snout and you will see dozens of small pores. They lead to jelly-filled tubes called the ampullae of Lorenzini, named for the Italian doctor who described them in 1678. For 300 years nobody knew what they were for. Then experiments showed they detect electricity. Every living animal gives off a faint electric field from its muscles, even when it lies still. In tests, sharks and rays responded to voltage gradients of five billionths of a volt across a centimeter. A flounder hiding under sand still gives off the faint field of its muscles, and the shark finds it.

Hammerheads take this furthest. The underside of the wide head is studded with electric sensors. The shark sweeps it across the sea floor like a metal detector, looking for stingrays buried in the sand. Then it uses the head to pin the ray down while it bites. Hammerheads also get superb depth perception from eyes set so far apart, and because the two fields of view overlap behind the head, a hammerhead can see all the way around itself, with blind spots only straight above and below.

Feeling the water

Down each side of a shark runs a line of tiny fluid-filled canals called the lateral line. It feels pressure changes in the water, so a shark senses a struggling fish, or a swimmer, from the ripples it makes. Sharks also hear well, especially low sounds, and in a field test off Florida blacktip sharks turned toward a sound from 243 ft (74 m) away, almost the length of a football field.

Eyes made for the dark

Behind the retina of a shark's eye lies a layer of mirror-like plates called the tapetum lucidum. It bounces light back through the eye for a second pass, the same trick that makes a cat's eyes shine in headlights. In dim water a shark reads every photon twice. Night sharks, which rise from the deep after dark, have oversized eyes with a vivid green shine.

A compass in the head

Sharks make some of the longest journeys in the sea with no landmarks in sight. In 2021, scientists exposed bonnethead sharks in a tank to magnetic fields that mimicked places hundreds of kilometers away. The sharks turned to swim "home." It was the first solid proof that sharks use the Earth's magnetic field as a map, at least for places they know.

The Eight Orders of Sharks

Scientists sort the 530-plus shark species into eight big groups called orders. Some scientists count nine, giving the two bramble sharks an order of their own. You can tell most of them apart by counting fins and gill slits and looking at the mouth. The biggest order holds about 300 species. The smallest holds seven.

A few of these groups will surprise you. The whale shark, the biggest fish in the sea, belongs with the nurse sharks and the wobbegongs, the carpet sharks that lie on reef floors. The flattened angel sharks look like rays but are sharks. The frilled shark, with its eel body and 300 needle teeth, belongs to the oldest order of all, a group already swimming 195 million years ago, before most dinosaurs.

Every species has its own page in the making. The full list of shark species is coming soon, with every order, family and species named.

Sharks by the Numbers

Sharks hold some of the most extreme records in the animal kingdom: the biggest fish, the longest life of any vertebrate, the slowest heartbeat and one of the hardest bites. Here are the record holders and the numbers behind them.

The biggest and the smallest

The whale shark is the largest fish alive. The biggest one reliably measured was 61 ft 8 in (18.8 m) long, longer than a school bus. Yet it eats some of the smallest things in the sea, straining plankton through a mouth up to 5 ft (1.5 m) wide. Its throat is only a few inches across, so anything big gets spat out. The second-largest fish is also a shark and also a plankton eater, the basking shark, at about 40 ft (12 m).

At the other end is the dwarf lanternshark of the deep Caribbean. It is fully grown at about 8 in (20 cm), smaller than many goldfish, and it glows along its belly. You could hide the smallest member of the ocean's most feared family in a coat pocket.

The three biggest sharks eat the smallest food. Of more than 530 species, exactly three gave up hunting for plankton, and they are the three giants.

The oldest

In 2016, scientists dated proteins in the eye lenses of 28 Greenland sharks and found the species lives at least 272 years. The oldest, a female just over 16 ft (5 m) long, was about 392 years old. She was born before the Pilgrims landed. Greenland sharks grow about a centimeter a year. Their hearts beat about six times a minute in the near-freezing water, and females do not have their first pup until about 150. A great white, by comparison, lives about 70 years and whale sharks 80 to 100 years or more.

The fastest and the strongest

The fastest shark is the shortfin mako, a torpedo of a fish with a crescent tail and a warm body. It runs down tuna and swordfish in the open ocean. Its bursts are estimated at about 70 km/h (45 mph); the fastest speed reliably clocked is about 50 km/h (31 mph). The hardest bite for its size belongs to the bull shark. A 2012 study calculated that its back teeth can deliver nearly 6,000 newtons, about 1,300 pounds of force, the most for body size of any shark tested. A computer model gives the biggest great whites about 1.8 metric tons of force. The same model put the extinct megalodon's bite at up to about 41,000 pounds of force, several times that of Tyrannosaurus rex.

The Life of a Shark

Sharks are born in three different ways, grow up slowly, eat almost everything the sea offers and travel farther than most birds. And nearly all of them do it alone from the day they are born.

Three ways to be born

Some sharks lay eggs. The pup grows for months inside a tough, leathery egg case, which beachcombers call a mermaid's purse. The Port Jackson shark lays a spiral case shaped like a screw, which the mother wedges into rock cracks so the waves cannot pull it out. Bamboo shark embryos can sense a predator's electric field through the case and freeze until it passes.

Most sharks give birth to live pups. In many species the eggs simply hatch inside the mother. In sand tiger sharks, the first pup to hatch in each womb eats its brothers and sisters, so each mother delivers exactly two large, battle-tested pups. In hammerheads, bull sharks and blue sharks, a cord joins each pup to its mother through a placenta, much as in mammals. Blue sharks usually bear 25 to 35 pups, and litters of up to about 135 have been recorded. One whale shark caught off Taiwan in 1995 held about 300.

A few sharks need no father at all. In 2001 a hammerhead pup appeared in a Nebraska zoo tank that held only females. DNA tests proved it was a virgin birth, called parthenogenesis. In Australia, a zebra shark named Leonie bred with a mate for years, was separated from males, and then produced healthy young alone. Female sharks of several species can also store sperm for years; one bamboo shark produced a pup after 45 months of isolation.

Growing up alone

Shark pups are born fully formed, with teeth, and are immediately on their own. No shark mother guards or feeds her young. Instead, many species give birth in shallow nurseries, lagoons, estuaries and mangroves, where big predators cannot follow. Young lemon sharks at Bimini in the Bahamas spend years among the mangrove roots, and scientists there found they prefer certain companions and learn tasks faster by watching experienced sharks. Baby bull sharks grow up in river mouths where the water is too fresh for most sea hunters.

Sharks grow slowly and start families late. A great white is not ready to breed until its late twenties or early thirties. A Greenland shark waits about 150 years. Then the litters are small and the pregnancies long. The frilled shark is estimated to carry its young for about 3.5 years. This slow life is why shark populations empty quickly when they are overfished and refill slowly, if at all.

What sharks eat

Almost every shark is a hunter. They eat fish, squid, crabs, seals, sea turtles, seabirds and other sharks. Tiger sharks eat nearly anything. Their stomachs have yielded license plates and tires, which earned them the nickname "wastebaskets of the sea." Great whites ambush seals from below, launching clear out of the water at about 40 km/h (25 mph). The cookiecutter shark, only 20 in (50 cm) long, twists neat round plugs of flesh out of tuna, whales and even the rubber domes of submarines.

Three sharks gave up hunting altogether. The whale shark, the basking shark and the megamouth filter plankton, and they are the three largest sharks alive. A basking shark cruising with its mouth open strains about 1,800 metric tons of water an hour, close to an Olympic swimming pool. The bonnethead, a small hammerhead, is the one shark known to digest plants. Seagrass can make up more than half of what it swallows, and feeding trials in 2018 showed it digests about half of that.

Sleep and company

Sharks do rest, and some seem to sleep. Nurse sharks spend the day heaped under ledges, sometimes dozens deep, and return to the same spots again and again. Draughtsboard sharks studied in New Zealand in 2022 showed the lower energy use and flat posture of true sleep, some of them with their eyes open. Sharks that must swim to breathe seem to rest while gliding. And sharks are less solitary than their reputation. Lemon sharks keep friends, sevengill sharks hunt seals in loose packs, and scalloped hammerheads gather in schools of hundreds.

Where sharks live

Sharks live in every ocean, from under the Arctic ice to the tropics. They live from the surf line down to 3,700 m (12,100 ft), where the Portuguese dogfish hunts in freezing blackness. Bull sharks swim far up rivers. One was caught near Alton, Illinois, in 1937, more than 1,000 miles (1,600 km) up the Mississippi, and the "landlocked" sharks of Lake Nicaragua turned out to be bull sharks commuting from the Caribbean. In the Solomon Islands, scientists filmed hammerheads and silky sharks living inside the acidic, boiling plume of Kavachi, an active underwater volcano.

Sharks also travel. A great white named Nicole, tagged in South Africa, swam to Australia and back, about 12,400 miles (20,000 km), in under nine months. White sharks from California gather every year in a remote patch of the mid-Pacific that scientists nicknamed the White Shark Café, diving hundreds of times a day. Whale sharks cross oceans to arrive exactly when coral spawns off Australia or fish spawn off Mexico, the largest gatherings of giant fish on Earth.

Sharks and People

People have feared sharks, worshipped them, worn their teeth, lit lamps with their oil and turned them into movie monsters. The real history is stranger and kinder than the movies.

Fossils and tongue stones

Because shark skeletons are cartilage, whole fossil sharks are rare, but their teeth are everywhere. For centuries Europeans dug up fossil shark teeth, called them "tongue stones," and wore them as charms against poison, believing they fell from the sky or grew from dragons' tongues. In 1666 a Danish scientist named Nicolas Steno dissected the head of a great white caught near Livorno, Italy, and showed that tongue stones were shark teeth. It was one of the founding moments of the science of fossils.

The oldest fossil sharks come from rocks about 450 million years old. One of the best preserved, Cladoselache, was buried in the shale under what is now Cleveland, Ohio, about 370 million years ago, skin and muscle included. The strangest, Helicoprion, was a cartilaginous fish from 270 million years ago, closer to the chimaeras than to true sharks. It grew a spiral of teeth like a circular saw blade in its lower jaw. Scientists argued for a century about where on the animal the spiral went until CT scans settled it in 2013.

Megalodon

The largest shark that ever lived was Otodus megalodon, which hunted the world's oceans from about 20 million to 3.6 million years ago. It is known mainly from teeth, some as big as a human hand. A 2025 study by 28 specialists put its largest possible size at about 80 ft (24.3 m) and some 94 metric tons, with a slimmer body than a great white's. Newborn pups were already 12 to 13 ft (3.6 to 3.9 m) long. Megalodon was not the great white's ancestor. The two came from separate lines, and megalodon's line ended. When the oceans cooled and its prey moved away, it vanished.

Sharks in human hands

In Hawaiian tradition certain sharks were ʻaumākua, ancestral guardian spirits of particular families, fed and respected and never hunted by those they protected. Elsewhere people put sharks to work. Dried shark skin, shagreen, was the sandpaper of cabinetmakers for centuries; a study of a 1711 Stradivari cello found what looks like a shark denticle in the varnish. Before petroleum, oil from shark livers lit lamps, tanned leather and greased machines. In World War II a whole fishery rose and crashed on the vitamin A in shark liver oil, until chemists learned to make the vitamin in 1947.

Jaws and the real numbers

In 1975 the film Jaws became the first summer blockbuster and the first movie to earn more than 100 million dollars at the North American box office. It fixed the shark in the public mind as a man-hunting monster. Its author, Peter Benchley, spent the rest of his life regretting the panic and campaigning to protect sharks.

The real numbers are small. The International Shark Attack File at the Florida Museum of Natural History counts about 60 unprovoked shark bites a year worldwide, out of billions of visits to the sea. Its five-year average is 61 bites and eight deaths; 2025 brought 65 and nine. It puts an American's lifetime odds of dying from a shark bite at about one in 4.3 million. Most bites are a single bite, after which the shark lets go. Research that modeled a young great white's eyesight found a surfer paddling overhead looks much like a seal from below. Malaria, carried by mosquitoes, kills about 608,000 people a year. In the United States lightning kills 20 to 25 people a year; sharks kill about one every other year.

For every person killed by a shark, people kill more than 10 million sharks.

A Shark Timeline

Thirteen moments, from the first shark scales to the law that closed the fin trade.

1. 450 million years ago

   The first shark scales

   Tiny tooth-like scales in rocks from the Ordovician period are the oldest signs of sharks. The first trees were still some 65 million years away.

2. 370 million years ago

   Cladoselache

   An early shark preserved whole, skin and muscle included, in the shale under what is now Cleveland, Ohio.

3. 270 million years ago

   The buzz-saw jaw

   Helicoprion, a shark relative, grew a spiral of teeth like a saw blade in its lower jaw. CT scans settled where it sat in 2013.

4. 3.6 million years ago

   Megalodon dies out

   The largest shark that ever lived disappears as the oceans cool and its prey moves away.

5. 1569

   The word "shark"

   A big shark caught in the English Channel is shown in London. Sailors who had sailed with John Hawkins call it a "sharke," the first widely printed use of the word.

6. 1666

   Tongue stones explained

   Nicolas Steno dissects a great white's head in Italy and shows that "tongue stones" are fossil shark teeth.

7. 1678

   The electric pores

   Stefano Lorenzini describes the jelly-filled pores on a shark's snout. Their job, sensing electricity, stays a mystery for 300 years.

8. 1937

   A shark in Illinois

   Fishermen catch a bull shark near Alton, Illinois, about 1,000 miles (1,600 km) up the Mississippi River.

9. 1975

   Jaws

   The first summer blockbuster makes the shark a movie monster. Its author later spends his life defending real sharks.

10. 2001

    Virgin birth

    A bonnethead pup is born in a Nebraska zoo tank holding only females, the first proven shark parthenogenesis.

11. 2009

    The first shark sanctuary

    Palau bans all shark fishing in its waters, the first country to do so. Dozens of countries follow.

12. 2016

    The 400-year shark

    Eye-lens dating shows Greenland sharks live at least 272 years, the longest of any animal with a backbone.

13. 2022

    The fin trade regulated

    CITES adds dozens of requiem sharks and hammerheads to its trade lists, and the United States bans the sale of shark fins.

Sharks Today

The animals that outlasted five mass extinctions are now struggling with a sixth, and this one is made of fishing gear. The good news is that the world has started to notice, and sharks recover where they are protected.

The toll

Scientists estimate that fishing kills about 80 million sharks a year, and the number has not fallen even as laws against finning multiplied. Finning is cutting off a shark's fins, often while it is alive, and throwing the body back; the fins are sold for soup. Many more sharks die as bycatch, caught by accident on hooks and in nets set for tuna and swordfish. Because sharks grow slowly and have few young, they cannot replace losses like that.

The result shows in the Red List kept by the IUCN, the International Union for Conservation of Nature. Its assessment of all 1,199 known sharks, rays and chimaeras lists 391 species as threatened with extinction. Counting the species too little known to judge, the IUCN estimates the true share at more than one in three. Oceanic sharks and rays, the open-ocean species, declined by about 71 percent between 1970 and 2018. The angel shark, once common from Norway to the Canary Islands, has vanished from about 90 percent of its range.

What is being done

Palau, a Pacific island nation, banned all shark fishing in its waters in 2009, creating the world's first shark sanctuary. The Maldives, the Bahamas and more than a dozen other countries followed. In November 2022 the countries of CITES, the treaty that controls trade in wild species, added 54 requiem sharks and the last six hammerheads to its protected lists. By conservation groups' estimate, about 90 percent of the shark species in the international fin trade now need permits. In December 2022 the United States banned the buying and selling of shark fins nationwide.

Money helps too. Shark tourism, divers paying to swim with sharks, is worth hundreds of millions of dollars a year worldwide. A study in Palau valued a single living reef shark at about 1.9 million dollars over its lifetime to the tourist economy, against a few hundred dollars dead. And sharks keep the ocean healthy. Tiger sharks in Shark Bay, Australia, protect seagrass meadows by keeping grazing turtles and dugongs on the move. In the Bahamas, tiger sharks fitted with cameras helped scientists map the largest seagrass meadow on Earth in 2022.

How scientists study sharks

Much of what is on this page was learned in the last 30 years, from tags. A satellite tag bolted to a dorsal fin reports a shark's position every time the fin breaks the surface. That is how Nicole's trip to Australia and the White Shark Café were found. Acoustic tags ping to underwater receivers. Cameras strapped to tiger sharks mapped seagrass. Whale sharks are identified by their spots using a star-mapping algorithm written for the Hubble Space Telescope. And in 2020 radiocarbon from Cold War bomb tests, trapped in whale shark backbones, proved that each growth ring marks one year.

Shark Myths and the Truth

Few animals carry as many myths as sharks. Here are the eight you will hear most, and what the science says.

Sharks at a Glance

Thirty facts to remember, one line each.

• Sharks are fish with skeletons made of cartilage, the flexible stuff in your ears and nose.
• They belong to the class Chondrichthyes with rays, skates and chimaeras.
• There are more than 530 living species in eight orders.
• Sharks appeared about 450 million years ago, some 65 million years before the first trees and 200 million years before dinosaurs.
• They have survived every mass extinction since they appeared, five by the Natural History Museum's count.
• A shark has five to seven pairs of gill slits; most have five.
• Shark skin is made of tiny tooth-like scales called dermal denticles.
• Shark teeth are not rooted in bone; new rows move forward to replace lost ones.
• A big shark may use 30,000 teeth in a lifetime.
• Sharks have no swim bladder; an oily liver, up to a quarter of body weight, keeps them afloat.
• The ampullae of Lorenzini on the snout sense electric fields as weak as five billionths of a volt.
• Sharks smell in stereo, turning toward the nostril that catches a scent first.
• Great whites, makos and salmon sharks keep parts of their bodies warmer than the sea.
• The whale shark is the largest fish alive, up to 61 ft 8 in (18.8 m).
• The dwarf lanternshark, about 8 in (20 cm), is the smallest.
• The shortfin mako is the fastest shark.
• The Greenland shark lives at least 272 years and has her first pup at about 150.
• Only three sharks eat plankton: the whale shark, the basking shark and the megamouth.
• Sharks are born in three ways: from egg cases, from eggs that hatch inside the mother, or fed through a placenta.
• Sand tiger pups eat their siblings before birth.
• Virgin birth (parthenogenesis) was first proven in a bonnethead shark in Nebraska in 2001.
• A great white named Nicole swam from South Africa to Australia and back, about 12,400 miles (20,000 km), in under nine months.
• Bull sharks swim up rivers; one was caught near Alton, Illinois, in 1937.
• The word "shark" entered print in 1569; its origin is unknown.
• Fossil shark teeth were called tongue stones until Nicolas Steno explained them in 1666.
• Megalodon, the largest shark ever, died out about 3.6 million years ago.
• Jaws (1975) was the first summer blockbuster.
• Sharks kill about eight people a year worldwide; people kill about 80 million sharks.
• About one in three shark and ray species is threatened with extinction (IUCN).
• Palau created the world's first shark sanctuary in 2009; the United States banned shark fin sales in 2022.