Sharks :: Papers

INTRODUCTIONAlthough sharks belong to the class Chondrichtyes, there atomic number 18 many assorted types. Sharks arose about 350 million years ago and postulate remained virtually unvarying for the past 70 million years and still comprise a dominant group. It is thought that sharks al about certainly evolved from placoderms, a group of stark(a) jawed fishes. It took a long series of successful and unsuccessful mutations with fin, jaw positions etc to seduce us all the different designs of sharks around today. When asked to draw a shark, most people would draw a shape along the lines of the whaler shark family, tigers or a mackeral shark such as a porbeagle. all the same many people do not realize the sheer kind in the shape of sharks, or that rays are really sharks. Seldom does such an animal inspire such a variety of emotions reflecting a miscellany of fascination, awe and fear. Sharks have occasionally exacted a terrible price from piece who have trespassed on their ter ritory. No better understood than the ocean that they inhabit, these creatures should be regarded in the same way as lions, tigers, and bears as dangerous, predatory provided nonetheless magnificent animals. Different Types of Sharks Living sharks are divided into cardinal major orders, each easily recognizable by certain international characteristics. Each order contains one or more minisculeer groups, or families. In all there are 30 families of sharks and they contain the 350 or more different kinds or species of sharks. The eight major orders of sharks include the Squantiformes, Pristiophormes, Squaliformes, Hexanchiformes, Carcharhiniformes, Lamniformes, Orectolobiformes, and the Heterodotiformes. The orders have distinguishing characteristics that fit in each. The Squantiformes normally have flat bodies that are ray-like with mottle dorsal surfaces. These sharks have a short terminal mouth, which is armed with weeny impaling teeth. They also have a caudal fin, which has a lower lobe that is long-term than the upper lobe. Their pectoral fins extend forward over the ventrally direct gills. The Pristiophormes have more of an elongated snout, which is saw-like and edged with slender, needle-sharp lateral teeth. They have two dorsal fins and no anal fin. They use short transverse mouths and small cuspidate holding teeth in both jaws. Squaliformes have no anal fin as well, scarce their snout is not elongated, but is somewhat long. Many have powerful cutting teeth in both jaws. In some species these razor sharp teeth are in the lower jaw only and the upper teeth wait on to hold the food.