Shark Basics

Shark. A name that sends most people running, or swimming, for cover. But, what exactly is a shark?
                                   
Are sharks fish? Do they have bones?
Sharks are fish and they are in the cartilaginous fish family, a.k.a the Chondrichtyes. This means that, instead of bones, sharks have cartilage for every "bone" in their body except their teeth and jaws. Other members of the class Chondrichthyes are the rays, skates, and chimaeras.

How many types of sharks are there?

There are eight orders of sharks. The Hexanchiformes, the Squaliformes, the Pristiophoriformes, the Squantiniformes, the Heterodontiformes, the Orectolobiformes, the Lamniformes, and the Carcharhiniformes. In total, there is believed to be over 400 shark species.

A chart of all shark orders.

How long have sharks been around?

Fossil records show that sharks have been swimming in the seas for over 400 million years. That's about 175 million years before the dinosaurs! Since then the basic shark design has barely changed.

How long do sharks live?

Some sharks are so rare or just cannot be kept in captivity long enough that their longevity is still unknown. Their longevity also depends on the species of shark. Some sharks such as the smooth dogfish (Mustelus canis)  may only live 16 years, where as the porbeagle shark (Lamna nasus) may live as long as 46 years. The whale shark (Rhincodon typus) is thought to live to 100 years.

What does shark skin feel like?

Shark skin feels exactly like sandpaper. It is made up of tiny teeth-like structures called placoid scales, also known as dermal denticles.

Do sharks sleep?

It was once believed that sharks had to keep swimming to breath and could not sleep for more than a few minutes at a time. While some sharks do need to keep swimming, some species, such as the nurse shark (Ginglymostoma cirratum) use spiracles to force water over their gills allowing for stationary rest. Sharks do not sleep like humans, instead they have active and restful periods.

Can sharks hear?

Sharks have an excellent sense of hearing, though you can't see their ears since they have inner ears instead of big, non-streamlined, outer ears like humans have.

How many teeth do sharks have? 

Sharks can have up to 7 rows of teeth in their mouth at any one time. This is so they can lose a tooth and one will be right there to take its place. This way the shark is always ready to attack.

What is "electroreception"?

Electroreception is the sharks sixth sense. It's also the rarest animal sense. Only sharks and the duck-billed platypus of Australia are thought to have this sense. Here's how it works: All organs emit electrical signals. Sharks have special organs called the ampullae of Lorenzini that can detect these electrical signals. This allows sharks to pinpoint and locate the electric field- even if it's coming from an animal buried motionless on the seabed. The ampullae are delicate, jelly-filled pores on the snout. They are so sensitive they can detect electrical fields of one hundred-millionth of a volt.

I hope that answered all your sharky questions!

                                                                                                                                        

note: I do not own any of these pictures.