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Silurian Period |
 | | The Ordovician trilobites were more successful at exploiting new environments, notably reefs, but they too suffered a crisis, during the mass extinction at the end of the Ordovician. |
| | Some distinctive and previously successful forms such as the Trinucleoidea and Agnostoidea became extinct. |
| | Whiterock Fauna families, and in particular Silurian Fauna groups, can generally be traced only to the Early Ordovician, and in many cases they are entirely "cryptogenetic." These clades certainly had Cambrian forebears, but the fact that they have avoided detection is a strong indication that novel morphologies were being developed very rapidly. |
| www.peripatus.gen.nz /paleontology/Silurian.html (2626 words) |
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