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Ordovician
The Ordovician is a geologic period that lasted from 485 to 443 million years ago. In the Ordovician period trilobites and graptolites were common. Several mollusks evolved. The number of primitive fish and (sea) plants increased. Brown, Red and Green algae appeared. First fish with developed skeleton and muscles appeared. At the end of the Ordovicium there was a large mass extinction.
The Ordovician period in the geological timescale
See also the article about the Geological Timescale.
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