Cetacea Order
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 sound waves and focus them in order for them to become strong enough to
hear well. However, sound waves travel faster through the water than in the air,
and so the external ear was no longer needed, and is no more 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 only hear sounds tens of miles away, but it
can also discern from which direction the sound comes. Cetaceans use sound in
the same way as bats – they emit a sound, which then bounces off an object and
returns to them. From this, cetaceans can discern the size, shape, surface
characteristics and movement of the object, 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 prey in total darkness. It is so advanced that most
cetaceans can discern between prey and non-prey (such as humans or boats), and
captive cetaceans can be trained to distinguish between, for example, balls of
different 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 is becoming so popular on wildlife documentaries and
relaxation tapes. Feeding When it comes to food and feeding, this is where
cetaceans can be separated into two distinct groups. The ‘toothed whales’ or
Odontoceti have 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
this group include the Sperm Whale, dolphins and porpoises. The ‘baleen whales’
or Mysticeti do not have teeth. Instead they have plates made of keratin (the
same substance as our fingernails) which hang down from the upper jaw. These
plates act like a giant filter, straining small animals (such as plankton, krill
and fish) from the seawater. Cetaceans included in this group include the mighty
Blue Whale, the Humpback Whale, the Bowhead Whale and the Minke Whale.
