EXPLANATION OF ERA

The Paleozoic Era began about 544 million years ago and ended about 248 million years ago. Traces of life are much easier to find in Paleozoic rocks than in Precambrian rocks. Because warm, shallow seas covered large parts of the continents during much of the Paleozoic Era, many of the life-forms scientists know about were marine. Trilobites were common, especially early in the Paleozoic. Other organisms developed shells that were easily preserved as fossils. Therefore, the fossil record of this area contains abundant shells. However, invertebrates were not the only animals to live in the shallow, Paleozoic seas. 

MASS EXTINCTION

At the end of the Paleozoic Era was a mass extinction, most likely caused by a great climate change and lowering of sea level. Organisms, like the Hyolith to the left, went extinct, along with 90% of marine species and 70% of all land species.

---