Cetaceans Essay Research Paper Whales dolphins and

Cetaceans Essay, Research Paper

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.