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 ...

That's right, prehistoric marine worms could have made a significant contribution to the Great Ordovician Biodiversifiaction ...

This sea teemed with marine life, its abundance and diversity rivaling modern-day sea life. However, in the Ordovician, the creatures were invertebrates, or organisms lacking a backbone, such as ...

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.