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 first starfish. Nevertheless the trilobites remain abundant, with all the Late Cambrian orders continuing, and being joined by the new group Phacopida.
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| Ordovician period | ||
|---|---|---|
| Lower/Early Ordovician | Middle Ordovician | Upper/Late Ordovician |
| Tremadocian | Stage 2 | Stage 3 | Darriwilian | Stage 5 | Stage 6 Hirnantian |
