Sharks came from the first fish, which lived over 500 million years ago! These fishes had no jaws or teeth. Over the years, their bodies changed to look like sharks we know today. There are more than 350 different species of sharks. Sharks are cold-blooded. that means their body temperature changes with the outside temperature. Most live in warmer oceans, but some live in rivers, lakes, and even cold arctic seas. some sharks lay eggs; others give birth to live young. Some like the pygmy shark, are small enough to fit in your hand. Others, like basking and whale sharks, are among the largest animals in the ocean and can be more than 50 feet long! All sharks, however, have important things in common.
CARTILAGE
Sharks are not mammals. They are a special kind of fish. They belong to a group of marine animals called Chondrichthyes. Sharks don't have a skeleton made out of bone like most fish. Instead, they all have strong, rubber-like skeletons made out of cartilage. Cartilage feels like bone, but it's not a hard. Because cartilage is more flexible, sharks can turn quickly in the water. Cartilage is also lighter than bone. This makes it easier for sharks to swim. ( The sides of your nose and ear are made out of cartilage)
TEETH
Sharks have very rough skin that protects them from injury. It's covered in tiny ridges that are actually tiny teeth! A shark's skin can cause wounds if it brushes against a human or another fish. ( In some countries, shark's skin is used as sandpaper.)
SWIMMING
Sharks are powerful swimmers. They usually swim about one and half to three miles an hour. But they can swim very fast when they need to. Most sharks swim by moving their tails, or
CARTILAGE
Sharks are not mammals. They are a special kind of fish. They belong to a group of marine animals called Chondrichthyes. Sharks don't have a skeleton made out of bone like most fish. Instead, they all have strong, rubber-like skeletons made out of cartilage. Cartilage feels like bone, but it's not a hard. Because cartilage is more flexible, sharks can turn quickly in the water. Cartilage is also lighter than bone. This makes it easier for sharks to swim. ( The sides of your nose and ear are made out of cartilage)
TEETH
Sharks have very rough skin that protects them from injury. It's covered in tiny ridges that are actually tiny teeth! A shark's skin can cause wounds if it brushes against a human or another fish. ( In some countries, shark's skin is used as sandpaper.)
SWIMMING
Sharks are powerful swimmers. They usually swim about one and half to three miles an hour. But they can swim very fast when they need to. Most sharks swim by moving their tails, or