Cetaceans

Whales, dolphins and porpoises make up the classification order Cetacea,which contains two suborders, Mysticeti and Odontoceti.

The baleen whalesare members of the Mysticeti suborder, while the toothed whales, dolphinsand porpoises make up the suborder Odontoceti. Altogether, the two suborders contain eighty-one known species, separatedinto thirteen different families. In each family are a number of species, eachclassified further into ‘sub-families’, or genera, of which there are 40. What Are Cetaceans?There are many misconceptions about cetaceans (whales, dolphins andporpoises), 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 externalears, they walked on four legs, they beared live young.

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As mammals, cetaceans have these characteristics that are common to allmammals:* 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 thetail. The tail of a fish is vertical and moves from side to side when the fishswims.

The tail of a cetacean is horizontal and moves up and down instead.The Cetacean’s Adaptations for Sea LifeOver a period of millions of years, the cetacean returned to the sea – therewas more food there, and more space than on land. Because of thisincrease in space, there was no natural limit to the cetacean’s size (i.

e. theamount of weight its legs could hold) since the water provided buoyancy. Ithad no longer any need for legs.During this time, the cetacean lost the qualities that fitted it for landexistence and gained new qualities for life at sea. Its hind limbsdisappeared, its body became more tapered and streamlined – a form thatenabled it to move swiftly through the water.

For the same reason, most ofits 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 apropeller.As part of this streamlining process, the bones in the cetacean’s front limbsfused together. In time, what had been the forelegs became a solid mass ofbone, blubber and tissue, making very effective flippers that balance thecetacean’s tremendous bulk.

After the cetacean’s hair disappeared, it needed some way of preservingtheir body heat. This came in the form of blubber, a thick layer of fatbetween the skin and the flesh that also acts as an emergency source ofenergy. In some cetaceans the layer of blubber can be more than a footthick.

Breathing, Seeing, Hearing and EcholocationSince the cetacean is a mammal, it needs air to breathe. Because of this, itneeds to come to the water’s surface to exhale its carbon dioxide andinhale a fresh supply of air. Naturally it cannot breathe under water, so as itdives a muscular action closes the blowholes (nostrils), which remain closeduntil the cetacean next breaks the surface. When it does, the muscles openthe blowholes and warm air is exhaled.

To make this easier, the cetacean’s blowholes have moved to the top of itshead, 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 andvapourises as it meets the cold air outside. This is rather like when youbreathe out on a cold day and a small cloud of warm air appears. This iscalled the ‘blow’, or ‘spout’, and each cetacean’s blow is different in termsof shape, angle and height.

This is how cetaceans can be identified at adistance 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) havegood binocular vision forward and downward, but others with blunt heads(such as the Sperm Whale) can see either side but not directly ahead ordirectly behind.

The eyes shed greasy tears which protect them from thesalt in the water, and cetaceans have been found to have good vision bothin the water and out.Akin to the eyes, the cetacean’s ears are also small. Life in the seaaccounts for the cetacean’s loss of its external ears, whose function is tocollect sound waves and focus them in order for them to become strongenough to hear well. However, sound waves travel faster through the waterthan in the air, and so the external ear was no longer needed, and is nomore than a tiny hole in the skin, just behind the eye. The inner ear,however, has become so well developed that the cetacean can not onlyhear sounds tens of miles away, but it can also discern from which directionthe sound comes.Cetaceans use sound in the same way as bats – they emit a sound, whichthen bounces off an object and returns to them. From this, cetaceans candiscern the size, shape, surface characteristics and movement of theobject, as well as how far away it is. This is called sonar, or echolocation,and with it cetaceans can search for, chase and catch fast-swimming preyin total darkness.

It is so advanced that most cetaceans can discernbetween prey and non-prey (such as humans or boats), and captivecetaceans can be trained to distinguish between, for example, balls ofdifferent colours, sizes or shapes.Cetaceans also use sound to communicate, whether it be groans, moans,whistles, clicks or the complex ‘singing’ of the Humpback Whale that isbecoming so popular on wildlife documentaries and relaxation tapes.FeedingWhen it comes to food and feeding, this is where cetaceans can beseparated into two distinct groups. The ‘toothed whales’ or Odontocetihave lots of teeth that they use for catching fish, squid or other marine life.They do not chew their food, but swallow it whole. The cetaceans in thisgroup include the Sperm Whale, dolphins and porpoises.The ‘baleen whales’ or Mysticeti do not have teeth.

Instead they haveplates made of keratin (the same substance as our fingernails) which hangdown from the upper jaw. These plates act like a giant filter, straining smallanimals (such as plankton, krill and fish) from the seawater. Cetaceansincluded in this group include the mighty Blue Whale, the Humpback Whale,the Bowhead Whale and the Minke Whale.Theater Essays