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The Silurian
Silurian Marine Life
The Invasion of Land
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Silurian Marine Life
Marine life thrived and diversified during the Silurian; many forms were similar to those of the earlier Ordovician Period. Although the later Devonian Period is often called the “Age of Fishes,” the Silurian also was an important time in the evolution of this group. In particular, it was marked by the wide and rapid spread of jawless fishes (agnathans). Only two of their jawless descendants—lampreys and hagfishes—survive today, but many different kinds populated the Silurian seas.

Among the invertebrates, brachiopods were especially diverse and abundant. Many survived from the Ordovician, but other new forms evolved as well, so that brachiopods represented nearly 80% of all Silurian marine invertebrate species. Although the planktonic graptolites lost many species in the end-Ordovician mass extinction, they also remained abundant. The common genus Monograptus included many species that are useful today as biostratigraphic fossils. Tabulate and rugose corals, calcareous algae, stromatoporoids, and bryozoans formed shallow-water tropical reefs. Cephalopods, gastropods, and echinoderms were among the active predators of the time. Trilobites began to decline in diversity after having reached their peak in the Cambrian and Ordovician.

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