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Whales are descended from prehistoric land mammals

Posted in Animals, Nature, Sea, Wildlife on Thursday, 29 November 2012

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This edited article about whales originally appeared in Look and Learn issue number 789 published on 26th February 1977.

killer whale, picture, image, illustration

Killer whale by G W Backhouse

The sea may be the realm of the fishes, but, for sheer size, the real monarch of the oceans is a warm-blooded mammal – the whale.

Like the seals and their relatives, the whales are descended from land mammals. Millions of years ago, their ancestors must have begun to explore first the river mouths and coastal shallows, then the deeper waters, in their search for food.

Eventually there evolved that astonishing order of creatures the cetaceans, to which the general name of “whale” is normally given. It includes also the dolphins and porpoises.

The cetaceans are far more completely adapted for aquatic life than the seals. It is true that they must still return to the surface to breathe, but otherwise they are just as at home in the sea as the fishes.

In their external shape, the whales look very much like fishes. They have the same stream-lined body, tapering fore and aft. The front limbs have developed into fin-like flippers, like the pectoral fins of a fish. They also have a tail shaped not unlike a fish’s caudal fin. But in the case of the whale the tail’s surfaces are horizontal instead of vertical. An up-and-down movement of this tail provides the main motive power in the whale’s swimming action, the flippers giving balance and direction.

Most cetaceans have a large dorsal fin, but, like the two “flukes” that form the tail, it has no bony structure, being merely a tough fleshy growth. The “hind legs” of these mammals do not appear externally at all, though vestiges of them can be seen when a dead whale is dissected.

Cetaceans can be divided into two distinct sub-orders – those that have teeth, and those whose mouths are equipped instead with baleen (or “whalebone”) plates, Baleen is a shiny, horny but flexible substance.

The baleen plates in a whale’s mouth may number as many as 300 on each side. They are triangular in shape, and their edges are frayed to form bristles. The plates project downwards from the upper jaw. As the whale swims about, with its mouth open, it takes in mouthfuls of water, which it then expels through the baleen bristles. Minute crustaceans and other plankton in the water are trapped in the mouth by the bristles and swallowed.

It is tragic to think that many of the magnificent baleen whales used to be killed just to provide whalebone stiffeners for Victorian ladies’ corsets.

A baleen whale must require an enormous quantity of the tiny prey it feeds on, in order to maintain its great bulk. Yet this group includes the world’s largest living creature, the blue whale, which may grow to a length of 100 feet (30m), and reaches a weight of 150 tons. This dark slate-blue cetacean has been sighted in every ocean of the world.

The toothed whales vary greatly in the number of teeth they have. They may be very numerous, but some have as few as a single pair. The Arctic narwhal is one of these. In the male narwhal, one of the teeth grows forward into a grotesque “tusk”, several feet long, and spirally marked. Frightening though it looks, it is not known to be aggressive.

The toothed whales, as one might expect, go for bigger game than plankton. Their food is mainly fish and large crustaceans.

In size, the toothed whales cannot match the largest of the baleen species. But the biggest of them, the cachalot, or sperm whale, is still a formidable creature. The male exceeds 60 feet (20m) in length, though the female is considerably smaller.

The cachalot is readily recognised by its unusual square head and snout, which project forward over the mouth. Its staple diet appears to be the giant squid, which it hunts at great depths. Despite its tremendous strength and enormous teeth, the whale does not capture its prey without a struggle. Sperm whales often bear on their heads scars left by the squids’ powerful suckers.

Also among the toothed cetaceans are the dolphins. There are many species. Probably best known is the delphinus delphis, or common dolphin. This has been seen in hundreds, or even thousands, playing on the surface of the open sea. Characteristic of most dolphins is the beaked snout and dome-shaped brow.

One of the dolphin family that differs strikingly from the others in its way of life is the grampus, or so-called killer whale. This is the only cetacean to prey on warm-blooded creatures, and includes among its quarry seals, penguins and other sea-birds, and even other whales.

The killer, 30 or more feet long, is much larger than other dolphins, which may be as small as five feet in length. It has great speed and strength, its large dorsal fin helping to give it manoeuvrability.

Dolphins have for centuries been known to be highly intelligent, and in many cases ready to befriend the human race. Like the rest of the cetaceans, they seem to be able to communicate with one another.

Whales generally prefer cooler waters to warm, as their food is more plentiful in the former. Most species, however, migrate to temperate, or even sub-trophical, waters, to breed. As the young calf has not grown the thick layer of blubber, or fat, needed as insulation against cold, it would not survive in polar seas.

It is in the Arctic and Antarctic regions that most havoc has been caused among whales by whalers, who hunt them mainly for their blubber. Greenland whales and blue whales have suffered especially badly.

Cetaceans appear to have little sense of smell, adequate eyesight, and exceptionally acute hearing. There is no external ear, but the hearing aperture is protected during submersion by a “valve” system.

For breathing, baleen whales have two slits on top of their head, the toothed whales only one. A feature of whales’ behaviour is their habit of blowing out what looks like a spray of water when they return to the surface after diving. In fact it is simply breathing out, the water vapour in the breath becoming visible as it condenses in the air.

It is known that whales can withstand underwater pressure at depths of 900 metres and more. Their lung capacity allows them to stay submerged for nearly an hour.

An especially interesting fact is that they can resurface rapidly from great depths. Though their breathing system is basically the same as ours, they are not subject to the “bends”, the dangerous and sometimes fatal affliction that attacks human deep-sea divers who ascend too quickly.

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