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Seals' story written in their own hand.

Seals' story written in their own hand

In the company of mammalian paleontologists, a mention of the word "pinniped" can launch a debate that might gobble up an entire evening's conversation. Pinniped, or "fin-footed," refers to an informal group of mammals that includes only three surviving forms: seals, sea lions and walruses. All pinnipeds have four flippers, whose shape reflects how these originally land-based animals invaded the sea millions of years ago and evolved bodies better suited to a mostly aquatic lifestyle. Although scientists agree on that much, a controversy is now developing concerning the finer details of pinniped evolution.

For decades, most experts have accepted the theory that "true" seals (the ones without ears) evolved from weasel- or otter-lkie forms, while sea lions and walruses developed from bear-like forms. Such dual development is called dyphyletic evolution. Proponents of this theory say the originally dissimilar pinnipeds now resemble each other because they have all adapted to life in a special environment, namely water.

Andre R. Wyss of the American Museum of Natural History in New York City and several other experts are advocating the flip side of the argument: that all pinnipeds evolved from one landbased mammal that entered the sea, a process known as monophyletic evolution. Wyss bases his conclusions on a close examination of the bone structure within pinniped flippers. In the Aug. 4 NATURE, he reports that all pinnipeds share quite similar hand and foot structures -- ones that do not resemble those of other land or aquatic mammals. Such a similarity would be surprising if seals evolved from a separate line, because they have a unique swimming style, using their hind flippers for propulsion, while sea lions paddle with their front flippers, he says.

Will the monophyly theory draw converts? Lawrence G. Barnes, curator at the Natural History Museum of Los Angeles County, says there is a good deal of evidence in favor of Diphyly that proponents of monophyly have yet to address.
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Title Annotation:research on pinniped evolution
Publication:Science News
Date:Aug 13, 1988
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