What is a shark?
Cartilage skeleton
Sharks are distantly related to modern bony fishes and belong to a group referred to as the cartilaginous fishes. They are vertebrates but, unlike bony fishes which have a hardened skeletalon, sharks have a soft skeleton composed entirely of cartilage.
400 million years
Ancestral sharks first appeared around 400 millions years ago. Modern sharks appeared first around 200 million years ago, and are so well designed, they have changed little since that time.
Apex predator
Sharks are built for hunting and capturing prey. Most have a very powerful set of jaws set with a formidable array of sharp teeth. A highly developed sense of smell, hearing, and electromagnetic sensitivity give sharks unrivaled skill at finding prey.
Armor plated skin
Unlike bony fishes which have overlapping scales, sharks have placoid scales arranged side by side similar to tile floor. The scales often have raised, tooth-like, projections that make the skin feel very rough like sandpaper. Shark skin is very abrasive and divers have been know to get abrasions from bumping into them. Shark skin has also been used to cover the handles of Japanese samurai swords to give them a firm grip!
Teeth
Sharks have man rows of replaceable teeth. Some sharks have many hundreds of teeth in their mouths at any one time. Since a shark's only means of grabbing prey is with it's teeth, it must be able to replace them on a regular basis.
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