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.
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
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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.
see also Geological Time Scale.
Asimov, Isaac. Life and Time. Garden City, NY: Doubleday & Company, 1978.
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.
Gould, Stephen Jay, ed. The Book of Life. New York: W. W. Norton & Company, 1993.
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.
Permian period (pûr´mēən) [from Perm, Russia], sixth and last period of the Paleozoic era (see Geologic Timescale, table) from 250 to 290 million years ago.
Historical Geology of the Period
The Lower Permian
During the Permian period, changes in the earth's surface that had begun in the preceding Carboniferous period reached a climax. At the close of the Carboniferous, large areas of E North America were dry land. In the Lower Permian, sandy shales, sandstones, and thin limestones of the Dunkard formation (formerly called the Upper Barren measures) were deposited in the remaining submerged areas of West Virginia, Pennsylvania, and Ohio, but the continued rising of the land soon put an end to deposition. The Dunkard is the last Paleozoic formation of the E United States. More extensive deposits were formed in the West. Parts of Texas, Oklahoma, Kansas, and Nebraska were covered by an arm of the sea or possibly by one or more salt lakes or lagoons, now represented by masses of salt or gypsum in layers separated and overlaid by red beds. There are important Permian salt mines at Hutchinson and Lyons in Kansas and gypsum mines in Oklahoma, Texas, and Kansas. The longest marine submergence of the Lower Permian in North America was in W Texas and SE New Mexico, where there is a system of marine limestones and sandstones 4,000 to 6,000 ft (1,200–1,800 m) thick. The Cordilleran region was also submerged; here marine beds are more common toward the west, and land sediments, especially red beds, toward the east. The red beds are generally considered to be indicative of increasingly arid conditions in Permian times.
In Europe, the Lower Permian, or Rotliegendes [red layers], was marked principally by erosion from the Paleozoic Alps of the Carboniferous into the low-lying land to the north; the formations are chiefly shale and sandstone, with some conglomerate and breccia. Red is a prominent color for the beds. The Pangaea supercontinent formed from an aggregation of all continents at this time.
The Permian and late Carboniferous of the Southern Hemisphere were radically different from those of the Northern Hemisphere. Australia, S Africa, and South America experienced a series of glacial periods, as is shown by the presence of tillite and of conspicuous striations of the underlying rock formations. This condition prevailed also in India. Paleozoic glaciation in North America is suggested by the Squantum tillite near Boston, Mass. This glaciation and the aridity of which the red beds seem to be the result are the two most strongly marked characteristics of the Permian period.
The Upper Permian
In the Upper Permian practically all of North America was above sea level, and the continent was larger than at present. Toward the close of the Upper Permian the greatest earth disturbance of the Paleozoic era thrust up the Appalachian Mts. In Europe, the Upper Permian was a period of more extensive marine invasion; the Zechstein formation is predominantly limestone, though it includes rich deposits of copper, salt, gypsum, and potash. The Upper Permian beds of Germany were long the chief source of the world's potash.
Evolution of Plant and Animal Life
Many marine animals became extinct during the Permian, but there was at the same time an evolution to more modern types, a marked change in the insects, and a notable increase in numbers and varieties of reptiles mainly because of the continental changes. Among plants, Lepidodendron and Sigillaria became rare, but ferns and conifers persisted. The widely distributed "seed fern," Glossopteris, which was apparently successful in resisting glacial conditions, was the most conspicuous development in the Permian flora. The presence of Glossopteris in South America, Antarctica, Australia, and S Africa is a strong argument favoring the interconnection of these land masses in a large supercontinent during Permian time. The end of the Permian is marked in the fossil record by the most devastating mass extinction known.
In geologic time , the Permian Period, the last period of the Paleozoic Era , covers the time roughly 286 million years ago (mya) until 245 mya.
The Permian Period spans two epochs. The Early Permian Epoch is the most ancient, followed by the Late Permian Epoch.
The Early Permian Epoch is divided chronologically (from the most ancient to the most recent) into the Asselian, Sakmarian, and Artinskian stages. The Late Permian Epoch is divided chronologically (from the most ancient to the most recent) into the Kungurian, Kazanian, and Tatarian stages.
In terms of paleogeography (the study of the evolution of the continents from supercontinents and the establishment of geologic features), the Permian Period was dominated by the movements of the supercontinent Pangaea, that during the Permian Period was located along the equator. Plate tectonic activity along the western border of Pangaea formed an extensive subduction zone that survives today as a large number of volcanoes located around the Pacific rim (i.e., the Pacific "Ring of Fire").
Differentiated by fossil remains and continental movements, the Carboniferous Period (360 mya to 286 mya) preceded the Permian Period. In many modern geological texts, especially those in the United States, the time of Carboniferous Period is covered by two alternate geologic periods, the Mississippian Period (360 mya to 325 mya) and the Pennsylvanian Period (325 mya to 286 mya). The Permian Period is followed in geologic time by start of the Triassic Period of the Mesozoic Era . The largest mass extinction in Earth's history—a catastrophic extinction of marine life— marks the close of both the Permian Period and the Paleozoic Era. Accordingly, many fossils dated to the Permian Period are not found in Mesozoic Era formations.
The fossil record indicates that more than 95% of all Permian species became extinct at the close of the Permian Period. Alternative hypotheses integrate differently the effects of loss of marine habitat due to the continued fusion of continents into Pangaea.
There were a number of major impacts from large meteorites during the Permian Period. Although no crater has been specifically identified with the impact possibly associated with the mass extinction of species, indirect evidence in the form of catastrophically fused quartz crystals (shocked quartz) in area of Antarctica indicates that the crater measured approximately 300 mi (450 km) in diameter. Other but smaller impact craters dating to the Permian Period have been identified in modern Florida, Quebec, and Brazil.
Because of the fusion and confluence of continental land masses in Pangaea, locations as diverse as Texas (Glass Mountains), Nova Scotia (Brule Trackways), and Germany share a similar fossil record dating to the Permian Period.
See also Archean; Cambrian Period; Cenozoic Era; Cretaceous Period; Dating methods; Devonian Period; Eocene Epoch; Evolution, evidence of; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Miocene Epoch; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Phanerozoic Era; Pleistocene Epoch; Pliocene Epoch; Precambrian; Proterozoic Era; Quaternary Period; Silurian Period; Tertiary Period