The name shark came from the Mayan word ‘xook.’ The shark callers of Kontu in Papua New Guinea are the one who made people aware of the relationship of man and shark. In this time, sharks were not really ferocious, such that they were called sea dogs.

Shark has over streamed bodies. In this over streamed bodies, it has fully cartilaginous skeletons. Sharks have five to seven gills for respiration. Their skin has an outer protection called dermal denticles. This improves the fluid dynamics of the shark.

Sharks come in different sorts of shapes and also sizes. They start from dwarf lantern sharks to great big white sharks.

Sharks feed on squid, plankton and other fishes. They are found in salt and fresh water. They do not have swimming bladders. Instead, they rely on their large livers filled with oil for buoyancy. They sink when they stop swimming.

Sharks need to swim constantly to breathe. They don’t sleep often. There are species that has spiracles that gives more chances to have a stationery rest at the bottom of the ocean.

The life span varies per species. Most of them live from 20 to 30 years. Only spine dogfish has a record of more than one hundred years. Sharks are considered nature’s hardy predator. There have been recorded videos already capturing the viciousness of sharks.

Sharks have very powerful jaws, growing more than twenty thousand teeth in one lifetime. Shark teeth are easily replaced when lost. This is why it is easy for them to eat humans.

Sharks also prey on a lot of other fishes in the ocean. But no matter how aggressive and dangerous they look, there is one thing that sharks can not eat. That is a puffer fish. A puffer fish bloats like a balloon as a defense mechanism when they sense an imbalance in their surroundings. Its sharp needles hurt the mouth of a shark when they are swallowed.

The brains of sharks are mainly for smelling to locate their prey. This makes them good predators. Their eyes have mirror like layers that make them see clearly in murky waters. And they can smell their prey even from far distances.

The sharks have Ampullae of Rorenzini, which is an electro receptor organ. This receptor organ alerts or gives them a keen feeling of vibration whenever there is potential prey. Another thing that one should know is that sharks have great listening abilities that it can hear the sound of the prey even if the prey are miles away.

Sharks also have a unique boneless skeleton. Instead, these skeletons are composed of tough and elastic cartilage. Their body is rounded, tough-skinned and streamlined. This helps them swim very efficiently. They can move their bodies with great maneuverability. One thing that aids their swimming capabilities is an oversized liver that is full of oil. Swimming keeps a shark’s body from sinking.

There are many species under the shark family tree, each species having unique characteristics. One interesting kind of shark is the Swell Shark, commonly found in New Zealand. It emits sounds similar to a barking dog.

Lastly, another interesting fact about sharks is that most of them reproduce like humans. Some species lay eggs. But majority of sharks give birth to baby sharks. Mommy sharks can have six to twelve babies at one time. The tiger shark can give birth to as many as forty sharks in one pregnancy.