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When feet had seven toes.

When feet had seven toes

Paleontologits have discovered something unexpected at the end of a 360-million-year-old leg: two extra toes. Since the 1930s, scientits have believed that Icthyostega, one of the earliest known amphibians, crawled around on five-toed feet. But fossil finds from Greenland now indicate that Icthyostega had seven toes on each hind foot. What's more, fossils from Acanthostega, another primitive amphibian, reveal it had eight fingers on each forelimb, according a report in the Sept. 6 NATURE by Michael I. Coates and Jennifer A. Clack of the University of Cambridge in England.

These early amphibians lived at the end of the Devonian period -- a time when vertebrates were first making the transition from water to land. In fact, the Acanthostega fossil is the most primitive known limb. Judging from their skeletons, these amphibians spent most of their time in the water, Coates says.

Paleontologists have traditionally held that all land vertebrates followed a five-digit or pentadactyl pattern. Though many vertebrates, such as horses, have fewer than five digits, they evolved from pentadactyl forms. The new fossil finds compleent a previous discovery by Soviet scientists of another six-digited Devonian amphibian. Taken together, these fossils indicate that development in early land vertebrates followed a more flexible patter. While some amphibians had seve-toed feet, other members of the same species might have sported feet with six or eight toes, Coates says.
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Title Annotation:Icthyostega - primitive amphibian
Publication:Science News
Date:Sep 22, 1990
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