Sharks are fierce hunters of the sea, but not all of them are man-eating monsters - says Blix in his short article on sharks.

Sharks are fierce hunters of the sea, but not all of them are man-eating monsters.

They are fish, but quiet different from most of the fish that we see in rivers and ponds, or catch for food in the sea. 
The biggest difference is in their skeletons. Sharks' skeletons are made of cartilage (gristle) rather than bone. There are many other differences, some which seem to date back a very long time - 300 million years or more. 
So sharks are in some ways more "primitive" than bony fish. There are fewer different kinds alive today than there have been in the past, and nowhere near so many kinds as there are of bony fish. (How many different kinds of bony fish? About 20 000 have been discovered so far, and there are probably more undiscovered.)
However, sharks swim, hunt, catch their food, and in many other ways work just as well and efficiently as bony fish. 
They are not that dangerous as people try to make believe us. Sometimes they attack people, but that is because they need to hunt or even because they are scared 

Look at the following video, and you will believe it!

Blix

 

http://www.youtube.com/watch?feature=player_detailpage&v=WK2LpUoqX6A