Life at the start of the Ordovician remained confined to the seas with new animals evolving in place of those that didn't survive the Cambrian. Chief among them were the squidlike nautiloids ...

The Ordovician world was a watery one in which ... They come from arthropods — the group of animals including insects, spiders, scorpions, shrimp, cnidarians (jellyfish and corals), plus algae ...

The Paleozoic era's Silurian period saw animals and plants finally emerge on land. But first there was a period of biological regrouping following the disastrous climax to the Ordovician.