Evolution

The Evolution of Sharks



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The very word 'shark' conjures up thought of the Great White that became famous from the series of films called Jaws. There are however more than 350 different species of shark lurking in our oceans ranging in size from around 1 meter to 12 meters for a fully grown Whale shark which is the biggest of all sharks known to man.

Sharks have inhabited the earth for over 400 million years and were around before the dinosaurs roamed the earth. Sharks are so adept at hunting and feeding that they have not really evolved a great deal in the last 150 million years. Some sharks feed on plankton
as their staple diet whereas others feed predominantly on meat. With powerful bodies the shark can swim quickly towards its prey and strike with such ferocity that the victim has little chance of escape.

Sharks are so diverse in type that they can differ from species to species how they produce their young, they range in number from 1 to 100 pup sharks being born at any one time. There are 3 different ways in which they give birth to their 'Pups'. Some lay eggs in a safe place on the sea bed and will then discard them and have no maternal instinct towards ensuring the pup is safe whilst growing, its on its own! Some sharks eggs grow inside the mother shark and will hatch inside her and are born in the same way we humans are. Lastly, pup sharks can develop inside the mother shark like we do. Growing inside the womb to be born as a tiny version of themselves.

Over the centuries sharks have strengthened their hunting skills to be the most feared predator in the sea. Two thirds of the sharks brain is used to enhance its sense of smell to alert the shark that food is nearby. Others have the eyesight of a cat, having developed a mirror like screen over the eyes they can see quite clearly in the murky depths of the ocean. Sensors run along the sharks body, known as the 'Lateral line' which is covered with tiny hairs that sense tiny vibrations in the water to again let the shark know that dinner may be swimming by. The most amazing tool the shark has developed though is the power to feel electrical pulses in the water that are emitted by its prey, this is called the 'Ampullae of Lorenzini' and is a sensor used by a great number of sharks to enhance its hunting skills.

As we know from the films, Sharks have a vast number of teeth that are razor sharp to rip through even the tough skin of a passing seal. Combined with powerful jaws that are controlled by the lower jaw bone, the Shark has little difficulty piercing through the defenses of any oceanic species. Some sharks will lose teeth whilst attacking their prey but this is not a problem to them as they can use and grow up to 20,000 teeth in their lifetime.

Our fear of the shark has led us to hunt them in huge numbers and some species are struggling for survival. The myth that sharks will come into our shallows and eat humans is blown out of all proportion. Some sharks will confuse the splashing of our limbs and dark shadows on the water to be seals and will strike thinking they are bagging themselves a tasty seal for a meal. These attacks are very rare but get publicized greatly should they occur.

Sharks will eat just about anything and this is confirmed by the gutting of several sharks that were caught. *Opening the stomach has unearthed bottles of water, hens, whole reindeer, bottles of beer, a hand bag, and wrist watch but to name a few. There hunger leads them to chomp anything and everything that may be floating in the waters in which they reside.

In closing, we can now see that the shark is the ultimate feeding machine. With a range of skills that set it apart from the majority of sea creatures, the shark has had little need to evolve over the 400 million years that it has inhabited the planet. Let us hope that the misconception that we associate with these impressive fish does not impel us to continue hunting them down and depleting species until they become extinct. The oceans are their homes and we are merely guests in them.

* Information supplied from http://wrt-intertext.syr.edu/II2/samie.html

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