Paleozoic Era: Life

Two great animal faunas dominated the seas during the Paleozoic. The "Cambrian fauna" typified the Cambrian oceans; although members of most phyla were present during the Cambrian, the seas were dominated by trilobites, inarticulate brachiopods, monoplacophoran molluscs, hyolithids, "small shelly fossils" of uncertain systematic posiiton, and archaeocyathids. Although all of these except the archaeocyathids survived past the Cambrian, their diversity declined after the Ordovician. Later Paleozoic seas were dominated by crinoid and blastoid echinoderms, articulate brachiopods, graptolites, and tabulate and rugose corals.

By the end of the Ordovician, life was no longer confined to the seas. Plants had begun to colonize the land, closely followed in the Silurian by invertebrates, and in the Late Devonian by vertebrates. The early tetrapods of this time were amphibian-like animals that eventually gave rise to the reptiles and synapsids by the end of the Paleozoic. One of the earliest terrestrial tetrapod faunas known in the world is from Joggins, Nova Scotia.

Land plants evolved rapidly into the vacant niches afforded them on land. By the end of the Devonian, forests of progymnosperms, such as Archaeopteris dominated the landscape. By the end of the Paleozoic, cycads, glossopterids, primitive conifers, and ferns were spreading across the landscape.

The Permian extinction, 244 million years ago, devastated the marine biota: tabulate and rugose corals, blastoid echinoderms, graptolites, and most crinoids died out, as did the last of the trilobites. Articulate brachiopods and one lineage of crinoids survived, but never again dominated the marine environment.

Find out more about the Paleozoic paleontology and geology of North America at the Paleontology Portal.