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Paleozoic Life |
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| Updated: 4/23/98 |
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The Paleozoic starts with an explosion of animal diversity at the base of the Cambrian. Nearly all of the major metazoan phyla, plus some additional forms, appear in a short 40 million year time span. The fossil record is dominated by organisms with hard parts. First by primitive sponges and trilobites, then by brachiopods, bryazoans, crinoids, and corals. Our discussion of Paleozoic life begins with an examination of the Cambrian Explosion and then looks at changes in the marine biosphere, including evolution of the fishes. The middle Paleozoic is marked by another event that changed the face of the earth, the invasion of land by plants and animals. The invasion of land not only opened new opportunities for life, but also affected sedimentary processes and altered the composition of the atmosphere. Land plants and the first insects appear in the late Silurian. These organisms were followed by the amphibians in the late Devonian and the reptiles in the Carboniferous and Permian. The end of the Paleozoic is marked by the largest mass extinction recorded in the history of life. Around 95% of the marine species become extinct. Extinctions also occurred in land animal and plant groups, though do not appear to be as intense. There does not appear to be a single cause for this mass extinction. In general, it appears that closing ocean basins, anoxic ocean waters, fluctuating CO2 levels in the shallow oceans, intense climatic variations, and extreme vulcanism combined to make the earth less hospitable for life. Lecture Notes:
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