When most people think of sharks, they think of big, powerful predators, bristling with teeth and ready to explode into a killing frenzy at the mere scent of blood. And while some sharks are large and dangerous, others are small and shy, tiny and stealthy, or giant and peaceful. In fact, the truth about sharks is a lot more mysterious and incredible than anyone could possibly imagine. Take a look at these shark facts and see if you don't agree:
Shark Facts
Sharks and their relatives
- Scientists have described over 400 types of sharks swimming in the ocean today.
- The closest relatives of sharks are skates and rays (animals like stingrays and manta rays). There are more than 600 types of rays and skates known.
- Also closely related are the mysterious and rare chimaeras (ky-MARE-uhs), also called spookfish or ratfish. There are less than 50 known species of chimaera.
- Sharks, rays, skates, and chimaeras are called cartilaginous (cart-eh-LAJ-in-us) fish, because their skeletons are made of cartilage, which is the rubbery stuff you've got in the tip of your nose. Other fish, like goldfish or trout, are called bony fish because they have skeletons made of bone (like us).
- Scientists use the term chondrichthyan (con-DRICK-thee-an) for sharks and their relatives. It comes from the Greek words for "cartilage" and "fish". Similarly, bony fish are called osteichthyans (os-tee-ICK-thee-ans) from the words for "bone" and "fish".
Shark Senses
- Sharks have an incredible sense of smell. Some can detect blood even if it has been diluted by 10 million times as much water—meaning they could smell one drop of blood in an area the size of a swimming pool!
- Sharks' eyes are designed to see for long distances underwater. They have color-vision, and can see very well even in dimly-lit water.
- Sharks can hear very well, especially the ultralow frequencies of sound that carry underwater.
- Like all fish, sharks have a "lateral line" on each side of their bodies that can feel vibrations in the water. Predatory sharks are particularly good at sensing the thrashing of injured or helpless prey.
- Sharks also have a special "electroreception" sense, which allows them to detect the weak electrical charges that all animals make. This allows sharks to hunt prey that they can't see, like fish buried in the sand. It might even help them navigate using the earth's magnetic field.
Shark records
- Largest:
Today: The Whale Shark grows up to 46 feet long with a mouth up to 3 and a half feet wide. This gentle giant eats only plankton.
All time: The mighty Megalodon, or Megatooth Shark, is known only from partial remains, but it appears that this relative of the Great White might have grown up to 60 feet long with jaws four to five feet wide. It could have eaten the whales and dolphins that swam the seas between 25 and 3 million years ago.
- Smallest:
Today: Pygmy sharks and dwarf lantern sharks, both members of the dogfish family of sharks, only grow to be about 10 inches long
All time: Some fossil shark's teeth are so small that they can only be seen under the microscope. These could have come from sharks as small or smaller than today's smallest sharks, but there is no way of knowing whether the sharks they came from were fully grown.
- Fastest: The Mako is the fastest shark ever known, swimming at speeds of up to 22 miles per hour to catch quick-swimming fish like marlin, tuna, and swordfish.
Shark Tooth Hall of Fame
Sharks are amazing tooth factories—they have rows and rows of teeth in their mouths, so that when one breaks off or loses its edge, a new one is ready to take its place. Some sharks go through 20,000 teeth in a lifetime!
Different types of shark have very different types of teeth. Each tooth style is specially adapted for catching or eating particular types of food. Here are some of the more noteworthy examples of shark's teeth:
- Mega-tooth: the biggest and the baddest, Megalodon, whose name literally means "giant tooth", had triangular, serrated teeth up to 7 inches long.
- Scissor-tooth: Sharks of the genus Edestus had jaws like giant pinking shears. Their long serrated tooth batteries could have cut other fish in two. Scissor-toothed sharks lived 325 to 280 million years ago.
- Whorl-tooth: Whorl-toothed sharks had a spiral disc of teeth in their lower jaw, making them look like a cross between a shark and a buzzsaw. Some species of whorl-tooth had teeth up to 9 inches long and might have been bigger than a Great White. They lived between 280 and 225 million years ago.
- Petal-tooth: Petalodont sharks had large teeth that looked like artichoke petals! They might have used their teeth to gnaw on coral or sponges like Parrotfish do today. Petalodonts thrived before the Age of the Dinosaurs—between 345 and 225 million years ago.
- Cookie Cutter: The strange little Cookiecutter Shark was named because it takes round, cookie-shaped bites out of larger fish, dolphins, and whales. It has even been known to bite chunks of rubber from the hulls of submarines!
Shark Fin Hall of Fame
Some sharks stand out because of the unusual adaptations found in their fins and tails.
- Anvil-Fins: Extinct sharks like Stethacanthus and Akmonistion had fins on their back shaped like anvils covered in sharp, tooth-like denticles. They might have been used in courtship rituals, or they may have just made them very difficult to eat!
- Neck-Wings: Iniopterygians (in-ee-op-toe-RIDGE-ee-ans) had large, wing-like fins on their necks. They lived between 345 and 280 million years ago. Some scientists think they could have glided through the air, like flying fish today.
- Tail-Clubs: Thresher Sharks have huge tails that are as long as the rest of their body. They approach schools of fish and swing their tails like baseball bats, knocking their prey senseless.
Sharks and People
- Every year, sharks attack about 100 people worldwide. Only about 10 of these attacks are fatal. That's less than the number of people killed each year by lighting, bees, or falling appliances.
- Every year, people kill millions of sharks. Many of these sharks are trapped accidentally in nets set out for other fish. Huge numbers of sharks are killed so their fins can be used to make shark-fin soup. In some places, shark fins are so valuable that it isn't worth the trouble for fishermen to bring the whole shark back. Sometimes the fins are cut off while the shark is still alive, and it is tossed back into the sea where it slowly dies.
- Unlike other fish, which lay hundreds or thousands of eggs, sharks only have a few young at a time. Many sharks take several years to become mature. This makes it harder for sharks to repopulate an area after their numbers have been reduced.
- Sharks and their relatives have survived for over 400 million years. Today, many sharks are endangered and some species are nearly extinct. If you'd like to learn more about the troubles facing sharks, and what you can do to help protect these amazing animals, please take a look at these links:
