Interesting facts about sharks

Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. 

Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date from more than 420 million years ago.

Since then, sharks have diversified into over 470 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 ft). Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can survive in both seawater and freshwater. They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have several sets of replaceable teeth.
Well-known species such as the great white shark, tiger shark,

blue shark, mako shark, and the hammerhead shark are apex predators—organisms at the top of their underwater food chain.

Many shark populations are threatened by human activities.
Here are some interesting facts about sharks:

•  Baby Great White Sharks are known to eat each other while still in their mother’s womb and that when born they escape quickly as their mother often sees them as prey!
• 16-foot-long, 3500 pound, female Great White shark named Mary Lee being tracked while she swims up and down the East coast
• Great White Sharks congregate in the middle of the pacific ocean in an area known as the White Shark Cafe