Permian
The Permian period, 280 to 230 million years ago, was named for the Perm Province of the Ural Mountains in Russia. The Permian signaled the end of the "ancient life" Paleozoic era.
In the Permian, the close ties between geology and evolution were especially apparent. The two great land masses of the Paleozoic drifted close enough together to form one supercontinent, Pangaea. Collisions in the tectonic plates created extensive volcanic activity and heaved up the Urals, Alps, Appalachians, and Rocky Mountains. The shallow inland seas drained to leave deposits of gypsum and salt. Vast sand dunes throughout much of what is now North America and Europe were recorded by massive yellow sandstones (hardened sand dunes) that contained few fossils other than scorpions.
Great glaciers scoured the southern regions of Africa, India, and Australia, further inhibiting life. Conifers and a few cold-hardy plants grew along the fringes of the immense ice cap.
The long stable climate of the Carboniferous gave way to dryness, with severe fluctuations of heat and cold. Only in the tropics of Pangaea did anything remain of the great Carboniferous rain forests, and there insects and amphibians continued to evolve.
Insects, members of the arthropod or "jointed leg" animals whose ancestors were the first to explore both land and air, continued to flourish in every new ecological opportunity. Several new groups appeared—the bugs, cicadas, and beetles. Thanks possibly to their diminutive size and adaptable metamorphosis, in which young live and feed in a totally different
| Era | Period | Epoch | Million Years Before Present |
| Paleozoic | Permian | | 286 |
| Pennsylvanian | | 320 |
| Missipian | | 360 |
| Devonian | | 408 |
| Silurian | | 438 |
| Ordovician | | 505 |
| Cambrian | | 570 |
An amphibian fossil from the Permian era on display at the Field Museum in Chicago, Illinois.environment from adults, the arthropods became the most evolutionarily successful animals on Earth. Amphibians fared less well, mostly just hanging on in those areas still hospitable to their warm, moist requirements.
Many marine species thrived in the shallow seas. Thousands of types of sponges, corals, ammonites, bryozoans, brachiopods, and snails left their remains in the rocks that now make up the mountains of west Texas and southern New Mexico. Bony fishes remained plentiful. However, spiny fishes, the fleshy-finned rhipidistians (organisms who originally gave rise to amphibians), and the once-dominant trilobites disappeared.
Reptiles flourished in the semidesert regions that made up much of Pangaea. Their leathery-skinned, cold-blooded bodies were ideal for the hotter, drier climate. Reptile adaptations led to herbivores and insectivores who could exploit new food resources. As their legs continued to become stronger and more upright, the reptiles increased in body size and mobility. Coelorosauravus joined the flying insects, gliding from tree to tree by means of a sail-like membrane. And Mesosaurus, a 1 meter (3 feet) long fish eater, returned to living underwater. Virtually the whole of Pangaea was dominated by the reptiles.
However, all this exuberance ended. The close of the Permian was marked by the worst extinction ever recorded. More than 75 percent of all plant and animal groups disappeared forever from the land, and in the ocean only about 5 percent of existing species survived. As devastating as these losses were, evolution and extinction are a recurring theme: the emptying of habitats, the reshuffling of genes, and a new start. Survival of the fittest might really be said to be survival of the luckiest.
Geological Time Scale.
Bibliography
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Fortey, Richard. Fossils: The Key to the Past. Cambridge, MA: Harvard University Press, 1991.
———. Life: A Natural History of the First Four Billion Years of Life on Earth. New York: Viking Press, 1998.
Friday, Adrian, and David S. Ingram, eds. The Cambridge Encyclopedia of Life Sciences. London: Cambridge University, 1985.
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McLoughlan, John C. Synapsida: A New Look Into the Origin of Mammals. New York: Viking Press, 1980.
Steele, Rodney, and Anthony Harvey, eds. The Encyclopedia of Prehistoric Life. New York: McGraw Hill, 1979.
Wade, Nicholas, ed. The Science Times Book of Fossils and Evolution. New York: The Lyons Press, 1998.
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