SHARKS
In some form, sharks have been around for about 400 million years.
Even before dinosaurs roamed the earth, sharks hunted through the oceans! They're such good survivors that they've had little need to evolve in the last 150 million years.
These ancient predators fascinate adults and children alike.
Scientific Information: Sharks belong to the class of fish, Chondrichthyes.
SHARK TEETH
Sharks have the most powerful jaws on the planet. Unlike most animals' jaws, both the sharks' upper and lower jaws move.
A shark bites with it's lower jaw first and then its upper. It tosses its head back and forth to tear loose a piece of meat which it swallows whole.
shark teeth Each type of shark has a different shaped tooth depending on their diet (the shark in the photo is a great white -- you can tell he's a carnivore just by looking at those sharp, pointy teeth!).
A shark may grow and use over 20,000 teeth in its lifetime!
DINNER TIME
Normally, sharks eat alone. But sometimes one feeding shark attracts others. They swim up as quickly as possible and all begin to try to get a piece of the prey. They bite wildly at anything that gets in their way -- even each other.
The great white shark rarely partakes in feeding frenzies.
CARNIVORES
Almost all sharks are "carnivores" or meat eaters. They live on a diet of fish and sea mammals (like dolphins and seals) and even such prey as turtles and seagulls.
Sharks even eat other sharks. For example, a tiger shark might eat a bull shark, a bull shark might eat a blacktip shark and a blacktip shark might eat a dogfish shark!
The teeth of the carnivores are sharp and pointy. Their skeleton is made of cartilage instead of bone, which allows greater flexibility.
Their skin is made of denticles instead of ordinary fish scales. The denticles are constructed like hard, sharp teeth and help to protect the shark from injury.
GENTLE GIANTS
Not all sharks are fierce carnivores. Some are quite harmless. Oddly enough, the most harmless sharks tend to be the largest! The basking shark, the whale shark and the megamouth sharks all fit this description.
These huge sharks eat plankton, a tiny shrimp-like creature found in the ocean. To do this, they swim forward with their mouths wide open. "Gill rakers" at the back of their throat strain the tiny food from the water.
DANGEROUS PREDATORS
Think sharks are dangerous? The most dangerous sharks are the Great White shark, the Tiger shark, the Hammerhead shark, the Mako shark and the Bull shark. On average, there are only about 100 shark attacks each year and only 10 of those result in a human death.
You should check it out from their perspective, though! People kill thousands of sharks in a year for sport and for food. Shark skins are used to make products like any other leather would be. Up until the 1950's, shark livers were used as a vitamin A supplement. Shark fin soup and shark steaks are both eaten in many countries (Mako, seen in the top photo, is the most popular in the United States).
So... who's the dangerous predator?
SHARK BABIES
Baby sharks are called pups. Just like there are many types of sharks, there are also different ways that sharks come into this world. There are three ways that sharks are born:
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eggs are laid (like birds)
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eggs hatch inside the mother and then are born
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pups sharks grow inside the mother (like humans)
Sharks can have from 1 to 100 babies at a time, depending on the type of shark. The ones with pups that grow inside the mother have fewer babies at a time than sharks that lay eggs outside the body.
Sharks do not care for their babies after they are born, but they do search for a safe place where they can lay their eggs or give birth.
SUPER SENSES
One of the reasons that sharks are such successful predators is that they have such super senses.
Two-thirds of a shark's brain is dedicated to its keenest sense -- smell.
Some sharks have eyes similar to a cat. A mirror-like layer in their eyes allows them to see better in the water. This allows the shark to hunt in clear seas or murky water.
To top it off, sharks have a few unusual senses. For instance, they are able to feel vibrations in the water using a line of canals that go from its head to its tail. Called a "lateral line", these canals are filled with water and contain sensory cells with hairs growing out of them. These hairs move when the water vibrates and alerts the shark to potential prey.
Sharks also have a sensory organ called the "ampullae of Lorenzini" which they use to "feel" the electrical field coming from their prey.
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