Early Ordovician

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The Early Ordovician, also called the Lower Ordovician by geologists, is the first subdivision of the Ordovician period, and marked a great diversification in marine life, following the extinctions at the end of the Cambrian.

Trilobites are joined by many new types of organisms, including tabulate corals, strophomenid, rhynchonellid, and many new orthid brachiopods, bryozoa, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first starfish. Nevertheless the trilobites remain abundant, with all the Late Cambrian orders continuing, and being joined by the new group Phacopida.

The first land plants which were probably tiny non-vascular plants resembling present day liverworts also appeared during this epoch around 474 million years ago.

Although Crinoids appeared earlier in the Cambrian period they only began to become common during the Early Ordovician epoch.