Cetaceans Essays - Megafauna, Cetaceans, Cetacea, Whale, Free Essays

Cetaceans Essays - Megafauna, Cetaceans, Cetacea, Whale, Free Essays Cetaceans Whales, dolphins and porpoises make up the classification order Cetacea, which contains two suborders, Mysticeti and Odontoceti. The baleen whales are members of the Mysticeti suborder, while the toothed whales, dolphins and porpoises make up the suborder Odontoceti. Altogether, the two suborders contain eighty-one known species, separated into thirteen different families. In each family are a number of species, each classified further into 'sub-families', or genera, of which there are 40. What Are Cetaceans? There are many misconceptions about cetaceans (whales, dolphins and porpoises), the most common of which is the idea that cetaceans are fish. They're not - they are mammals, like you and me. Millions of years ago, they lived on land; their bodies were covered in hair, they had external ears, they walked on four legs, they beared live young. As mammals, cetaceans have these characteristics that are common to all mammals: * They are warm-blooded animals. * They breathe in air through their lungs. * They bear their young alive and suckle them on their own milk. * They have hair - though generally only a few 'whiskers'. Another way of discerning a cetacean from a fish is by the shape of the tail. The tail of a fish is vertical and moves from side to side when the fish swims. The tail of a cetacean is horizontal and moves up and down instead. The Cetacean's Adaptations for Sea Life Over a period of millions of years, the cetacean returned to the sea - there was more food there, and more space than on land. Because of this increase in space, there was no natural limit to the cetacean's size (i.e. the amount of weight its legs could hold) since the water provided buoyancy. It had no longer any need for legs. During this time, the cetacean lost the qualities that fitted it for land existence and gained new qualities for life at sea. Its hind limbs disappeared, its body became more tapered and streamlined - a form that enabled it to move swiftly through the water. For the same reason, most of its fur disappeared, reducing the resistance of the giant body to the water. The cetacean's original tail was replaced by a pair of flukes that acted like a propeller. As part of this streamlining process, the bones in the cetacean's front limbs fused together. In time, what had been the forelegs became a solid mass of bone, blubber and tissue, making very effective flippers that balance the cetacean's tremendous bulk. After the cetacean's hair disappeared, it needed some way of preserving their body heat. This came in the form of blubber, a thick layer of fat between the skin and the flesh that also acts as an emergency source of energy. In some cetaceans the layer of blubber can be more than a foot thick. Breathing, Seeing, Hearing and Echolocation Since the cetacean is a mammal, it needs air to breathe. Because of this, it needs to come to the water's surface to exhale its carbon dioxide and inhale a fresh supply of air. Naturally it cannot breathe under water, so as it dives a muscular action closes the blowholes (nostrils), which remain closed until the cetacean next breaks the surface. When it does, the muscles open the blowholes and warm air is exhaled. To make this easier, the cetacean's blowholes have moved to the top of its head, giving it a quicker chance to expel the stale air and inhale fresh air. When the stale air, warmed from the lungs, is exhaled it condenses and vapourises as it meets the cold air outside. This is rather like when you breathe out on a cold day and a small cloud of warm air appears. This is called the 'blow', or 'spout', and each cetacean's blow is different in terms of shape, angle and height. This is how cetaceans can be identified at a distance by experienced whalers or whale-watchers. The cetacean's eyes are set well back and to either side of its huge head. This means that cetaceans with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward, but others with blunt heads (such as the Sperm Whale) can see either side but not directly ahead or directly behind. The eyes shed greasy tears which protect them from the salt in the water, and cetaceans have been found to have good vision both in the water and out. Akin to the eyes, the cetacean's ears are also small. Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect