Sharks

Sharks, which comprise less than 1 percent of all living fish, they are widely considered to be the apex predators of the ocean; their spot is at the top of the food chain. When people think of sharks, they imagine a fearsome, aggressive great white, swiftly cutting through the water. However, not all sharks are like that; many aren’t aggressive at all. 400 species

Sharks have inhabited the ocean for over 400,000,000 (400 million) years. Comparatively, modern-appearing humans have only existed for 200,000 years, which means that humans have existed only 0.05% (or 1/2000) of the time sharks have. Despite their age, the sharks of today still look very similar to their ancient ancestors. Long before the dinosaurs, sharks evolved their basic powerful and streamlined body shape, which has since needed little modification. The modern typical shark has a streamlined and slender body with a longish snout and pectoral fins.

Sharks belong to the group of cartilaginous fish (fish with cartilage). The skeletons of cartilaginous fish are composed of cartilage (similar to the material found in the human ear and nose) instead of bone. Like all fish, sharks are aquatic, water-breathing vertebrates. However, unlike the large, bright scales commonly found on other types of fish, sharks are covered with small, tough scales, called denticles. Sharks also have powerful jaws, filled with rows and rows of teeth. It is not uncommon for a shark to lose many of its teeth in a lifetime - fortunately, they are continuously replaced by new ones: one shark may have as many as 30,000 teeth in a life time. Some experiments suggest that a shark’s tooth can last from under a month, to a year.

Half of the world’s shark species reach a maximum length of between 6 inches and 39 inches. More than 80% are smaller than an adult human, and only 4% are larger than 13 feet. However, the largest shark specie, the whale shark, can reach lengths of 40 feet. This incredible length also crowns the whale shark as the world’s largest fish.

The two largest shark species, the whale shark and the basking shark, feed on plankton. Both species have close to neutral buoyancy, allowing them to travel at slow speeds.

The ocean environment is fairly stable: it changes very little in temperature. However, it also requires animals to be both efficient and powerful to effectively swim. Water is roughly 800 times as dense as air. Moreover, there is low visibility, which has lead to the evolution of other sensory organs.

About the Author
Jacob Maddox manages content for Wildlife Animals http://www.wildlife-animals.com an educational wildlife and animal website. Jacob also guest writes for Dog Pound http://www.dog-pound.net