00:04Sharks are interesting animals.
00:07There are many kinds of sharks all over the world.
00:10There is so much to learn about them.
00:14A human has a skeleton inside his or her body.
00:18This skeleton helps the human move.
00:21It also protects the organs that make the body work.
00:25Sharks have skeletons too.
00:27Their skeletons are not made of bone like a human's.
00:31They are made of cartilage.
00:34Cartilage is a strong rubbery matter that is not as hard as bone.
00:40Sharks have fins that help them swim.
00:42Their fins also help them change directions and stay still.
00:46Most sharks have 8 fins.
00:49Each one is used for something different.
00:53How many kinds of sharks are in the ocean?
00:56There are more than 350 kinds.
00:59Their sizes and shapes are not all the same.
01:02However, most sharks have long thin bodies.
01:05They also have really strong jaws.
01:08What do they use their strong jaws for?
01:13Sharks use their strong jaws for eating.
01:15Most sharks eat fish and other animals in the water.
01:19The largest shark does not.
01:21It eats a small shrimp-like animal called krill.
01:26Sharks have lots and lots of teeth.
01:29When they bite, some teeth break.
01:31When teeth fall out, new ones move into place.
01:34Sharks lose and regrow teeth throughout their whole lives.
01:37One shark can go through 30,000 teeth in its life.
01:43Even though sharks have so many sharp teeth, they cannot chew.
01:47They bite and swallow.
01:49It takes a few days for the food to break apart.
01:52Sharks do not need to eat every day because they are still breaking down food.
01:59The shapes of shark teeth depend on the food they eat.
02:02Some sharks bite food so they need sharp pointy teeth.
02:06Other sharks crush shells so they need cone-shaped teeth.
02:11People like to collect shark teeth.
02:13They know how long a shark is by measuring its tooth.
02:17A 1-inch-long tooth comes from a 10-foot-long shark.
02:26Sharks have skin covered in millions of teeth like scales.
02:29These tiny scales point to the tail of the shark.
02:33Rubbing a shark from nose to tail feels smooth.
02:36Rubbing a shark from tail to nose feels rough.
02:41Sharks are very good at smelling things.
02:44They can smell blood that is miles away.
02:46Their noses help them find food.
02:50People used to think that sharks couldn't see well.
02:54Now we know that sharks have strong eyes.
02:56Their eyes change to help them see where they are swimming.
03:00They can even see in dark waters.
03:04Sharks can sense electricity in the water.
03:08They do this through tiny holes found all over their noses.
03:12Other animals give off electricity when they move or their hearts beat.
03:16Small waves leave their bodies and travel through the water.
03:20Sharks feel these waves.
03:22They use this sense more than their eyes when hunting.
03:27Sharks have a small opening on each side of their heads.
03:31This opening leads right into the inner ear.
03:34People think sharks can hear very well.
03:37They may even be able to hear noises miles away from them.
03:43Most shark fossils come from shark teeth.
03:46When a shark dies, the rest of its body falls apart over many years.
03:51All that is left are teeth.
03:53Shark fossils show that sharks have been on the earth for millions of years.
03:57Many people think sharks lived even before the dinosaurs.
04:03The Megalodon is a huge shark that lived a few million years ago.
04:08It was 59 feet long.
04:10That is so much bigger than the length of the great white shark.
04:14People think the Megalodon hunted whales for food.
04:18The Megalodon's teeth were much bigger than the teeth of great white sharks.
04:24With the Megalodon gone, the whale shark is now the largest shark in the world.
04:29It can grow to be 39 feet long.
04:32It can weigh as much as 47,000 pounds.
04:35That is super heavy.
04:39The great white shark is also a very large shark.
04:43It is one of the biggest in the world.
04:46It can grow to be 21 feet long and 4,500 pounds.
04:50A great white shark has about 300 teeth in the shape of triangles.
04:55The teeth are used for eating fish and other animals, like seals and sea lions.
05:02The tiger shark is a large shark too.
05:05It grows to a length of 18 feet and weighs over 2,000 pounds.
05:09It eats mostly bony fish, rays, squid, dolphins, seals, shrimp, and krill.
05:15One shark that is easy to spot is the hammerhead shark.
05:19Its head looks a bit like a hammer.
05:22The largest hammerhead sharks can grow to be 19 feet long.
05:26They can weigh over 1,000 pounds.
05:29They feed on fish, other sharks, octopus, and squid.
05:32They love to eat stingrays.
05:37With over 300 named sharks in oceans so far, could there be any more?
05:42Yes.
05:43New sharks are still being found in Earth's waters.
05:47What new sharks might still be undiscovered?
05:52Some sharks are in danger.
05:54They are hunted for food or for sport.
05:57Shark meat is a seafood found in places like Australia and Japan.
06:01Small sharks are sold at markets in India.
06:07Sharks are found all over the world.
06:09They come in many shapes and sizes.
06:12They are rulers of the seas.
