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Migrating squid drove evolution of sonar in whales and dolphins, researchers argue
Date:9/5/2007

thed whales, the sperm whale, grows up to 60 feet long and dives to 3,000 meters - nearly two miles - in search of squid. Though poorly known because they live entirely in the deep ocean, the many species of the beaked whale dive nearly as deep. Belugas and narwhals descend beyond 1,000 meters, while members of the dolphin family - porpoises, killer whales and pilot whales, for example - all can dive below the 200-meter mark where sunlight is reduced to darkness.

According to Pyenson, who focuses on the evolution of whales, the first whales entered the ocean from land about 45 million years ago, and apparently did not echolocate. Their fossil skeletons do not have the scooped forehead of today's echolocating whales, which cups a fatty melon-shaped ball that is thought to act as a lens to focus clicking noises.

Skulls with the first hints of a concave forehead and potential sound-generating bone structures arose about 32 million years ago, Pyenson said, by which time whales presumably had spread throughout the oceans. Whales had developed underwater hearing by about 40 million years ago.

According to Lindberg, whale biologists had various theories about echolocation, including that whales developed this biosonar soon after entering the water as a way to find food in turbid rivers and estuaries. The evolution of toothed whales, however, indicates otherwise. Whales first occupied the ocean, and only later invaded rivers. Other experts have proposed that development of echolocation coincided with global cooling around 33.5 million years ago, though a mechanism was not specified.

The most convincing explanation, that echolocation allowed whales to more efficiently find food in the darkness of the deep ocean, ignores the question of evolution.

"How did the whales know there was a large supply of food down in the dark"" asked Lindberg, noting that cephalopods are the most abundant and high-energy resource in the ocean, eaten by
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
Source:Eurekalert

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