For elephants, its not just their ears and trunk that make them uniq...( >Conclusions As a result of hi...)

As a result of his work, Dr. West has made a number of observations. Among them is the fact that the primary evolutionary response to the vulnerability of the pleural membranes is to replace these with plates of dense connective tissue. The obliteration of the pleural space by loose connective tissue, which is the most obvious anatomic peculiarity appears to be a secondary response brought about because the normal mechanism for providing lubricating fluid for the pleural membranes no longer exists, and there is apparently some advantage in allowing the membranes to slide over each other.

He also notes that the mechanical problem facing the elephant's diaphragm during snorkeling. This is because the pressure difference across the diaphragm is about 150 mmHg, and this has to be sustained for many minutes while the animal is walking under the surface of a river or lake. This is a far greater trans-diaphragmatic pressure than can be sustained by the human diaphragm.

There are relative pressure changes that occur when the elephant raises water in the trunk for drinking or washing. For example, if f the water is raised through 200 cm, the alveolar pressure must be 200 cm H2O below atmospheric pressure, and the relative pressures are essentially identical to those during snorkeling. Since the elephant can raise water in its trunk with its mouth open, it is known that the low pressure is not developed by the buccal (near its cheek) muscles. It could be argued that this behavior, which is frequent in the elephant, is an additional evolutionary pressure for the anatomic changes in the pleural space. However, raising water in the trunk only takes a few seconds, whereas snorkeling lasts for many minutes and is therefore a much greater potential problem. As indicated earlier, the snorkeling behavior may have developed when the animal lived in water, and this would provide a very strong evolutionary pressure.

Finally, Dr. West
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Contact: Donna Krupa
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American Physiological Society
26-Aug-2002