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'Living fossils' display unusual behavior.

"Living fossils' display unusual behavior

They swim backwards, they drift upside down, they even perform an underwater version of a headstand. Such are the antics that West German scientists observed when they set out in a submersible to study a primitive fish that was once thought extinct.

Sometimes called "living fossils,' these are the only remaining examples of cross-opterygians --an ancient line of fish that many scientists believe spawned the first tetrapods, or four-legged land animals. This is the first time scientists have observed them in their habitat, and there is hope that these fish, called coelacanths, will aid in understanding the vertebrate transition from water to land.

Paleontologists had believed that coelacanths died out around 60 million years ago, until a living specimen was discovered off the coast of Madagascar in 1938. Since then, scientists have studied the behavior of line-caught coelacanths by releasing them at the surface. But coelacanths normally live under great pressure at depths of 200 meters, and they die within several days of surface existence.

The West German scientists, from the Max Planck Institute in Seewiesen and the Zoological Institute of the University of the Saarland in Saarbruken, performed 40 dives near the Comore islands, which lie to the northwest of Madagascar. They observed six of the coelacanths for a total of 80 hours, capturing the sometimes inexplicable behavior of this nocturnal creature in still photography, videotape and film.

In the past, scientists had speculated that coelacanths might use a pair of pectoral fins and a pair of pelvic fins to crawl along the ocean bottom. The fins are connected to the body by fleshy lobes, which are believed to be the evolutionary forerunners of limbs.

The West German team found that "paired fins are not used for locomotion on the bottom such as crawling or stalking.' Yet a close analysis of the film did reveal that opposite pectoral and pelvic fins sometimes moved in synchrony, a pattern common to horses and other tetrapods but rare among fish, say the researchers in the Sept. 24 NATURE.

Other researchers question the relevance of this observed behavior, contending that coelacanths are distantly related to tetrapods, if at all. However, say the West German scientists, "Such coordination could indicate another preadaptation in the crossopterygian group that could have facilitated the transition to locomotion on land.'

Photo: Photographed in their native habitat, coelacanths average 1.5 meters long.
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Title Annotation:coelacanths
Author:Monastersky, Richard
Publication:Science News
Date:Oct 3, 1987
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