The archaic sponge reef-dwellers of the Cambrian gave way to bryozoans—tiny, group-living animals that built coral-like structures. Ordovician reefs were also home to large sea lilies ...

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 ... climax to the Ordovician. The recovery soon got under way in the oceans as climbing temperatures and rising sea levels reproduced the ...