Ordovician
For most of the Ordovician, life continued to flourish, but near the end of the period the EndOrdovician extinction event seriously affected planktonic forms like conodonts, graptolites, and some groups of trilobites. Brachiopods, bryozoans and echinoderms were also heavily affected, and the cone-shaped nautiloids died out completely, except for rare Silurian forms.