Ancestors of dolphins walked on land

Press, 9 August 1985, Page 18

Ancestors of dolphins walked on land

By

GEOFFREY TUXNICLIFFE

It is hard to comprehend that the ancestors of whales and dolphins were air-breathing animals primarily adapted for life on land. Whales, dolphins and porpoises — collectively referred to by zoologists as cetaceans — have within their flippers bones which compare with the bones of the wrists, hands, and fingers of land-dwelling vertebrate animals. For hind Limbs, cetaceans have little or nothing, because over the millions of years they have spent adapting to living in ’water they have all but lost every vestige of hind legs.

Some cetaceans have no trace of hind limbs, and some have only vestigial limbs and hip bones buried deep within their bodies. The remnant hip 'nones are clearly visible at the hinder end of the blue whale skeleton on display at the Canterburv Museum.

On rare occasions, sperm whales with well developed hind legs have been captured, providing a strange reminder of the distant oast.

In adapting to life in an aquatic environment, cetaceans have added something that might pass for a

new limb. Their tails have become broadly flattened with a large area that can push great quantities of water behind them. These are the flukes which, allied to powerful tails and body muscles, and the nature of the skin (which is able to dampen vibrations and turbulence at its surface), propel these streamlined creatures at high speeds with comparatively little effort. Dolphins can swim at 20 to 22 knots for long periods; even the huge blue and sperm whales have been recorded doing 20 knots in short bursts. The larger baleen whales have cruising speeds at probably between 5 and 12 knots, nei whales have on occasions been clocked in at S 5 knots. In me absence of fur which is useful for insulation in the air. cetaceans depend on a thick layer of fatty tissue — the blubber — between skin and muscle to keep them warm. Another important advantage of blubber is that it is

buoyant and helps keep whales and dolphins afloat. The thickness of blubber varies from one part of the body to another. The flippers and flukes have little or none of it on them and therefore these structures help whales and dolphins to control their body temperature. Besides its insulating and buoyant properties, blubber is also a food reserve for whales. .An important feature of cetaceans which they have in common with other mammals is that they are warm-blooded — their body temperature is about the same as humans. They also have to surface to breathe. Cetaceans give birth to live young and feed them on milk produced by the mammary glands. The teats, along with the sex organs and ears, do not protrude from the bodv.

Tnere are many amazing aspects of dolphin behaviour which make it clear "that they are highly intelliaenu Thev have an outstanding

ability to learn — an ability which can exceed the imagination of their trainers. Their brains are 40 per cent bigger than humans'.

Many studies have been made tc investigate tne runction of tne complicated range of sounds — the clicks and whistles — they produce. The clicks of the toothed whales, which are thought tc originate in the nasal sac and larynx, are used in echo location and the whistles m communication.

.Although there is some controversy about the existence of a language tn cetaceans, it has been oostulHied that rather than a "sound language" dolphins may communicate by sending out "sound pictures." This is in agreement with tne structure of their brains, a large percentage or which is for the analysis of sounds. .Anyone who has worked closely with cetaceans cannot help but be

impressed by their personality. They are gentle, affectionate, playful. and show compassion and loyalty to people as well as to each other.

It is disturbing, therefore, to read that at the July annual meeting of the 40-nation International Whaling Commission in Bournemouth. England, five countries objected to an international moratorium on commercial whaling. Conservationists worldwide are concerned about rhe depleted stocks of many species of whales. Indeed, unless full protection is given to whales, their future on this planet may be pretty bleak.