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Devonian period

The Columbia Encyclopedia, Sixth Edition

Devonian period , fourth period of the Paleozoic era of geologic time between 408 and 360 million years ago (see Geologic Timescale , table). It was named (1838) by the geologists Sir Roderick Impey Murchison and Adam Sedgwick for Devonshire, England, where they first investigated rocks formed during the period. The Devonian period was a time of great tectonic activity, as Laurasia and Gondwanaland drew closer together. Pangaea began to consolidate the plates containing North America and Europe (see plate tectonics ), further raising the northern Appalachian Mountains and forming the Caledonides in Britain and Scandinavia. For much of the Devonian, large areas of North America and Europe, and smaller parts of Africa, South America, and Australia were covered by seas, which withdrew during the Upper Devonian. The Cordilleran area of North America was submerged, depositing from 4,000 to 6,000 ft (1,200-1,800 m) of limestone and shale in Nevada and 2,400 ft (730 m) of quartzites and limestones in Utah. The Devonian period in Europe was marked by considerable volcanic activity and the deposition of two great rock systems: the marine formation of Devonshire, the Rhine valley, and Russia; and the Old Red Sandstone . The climate was relatively warm everywhere on the earth. The most notable Devonian animals were the jawed and bony fishes, which appeared in great numbers toward the close of the period. Conspicuous types were sharks, armored fishes, lungfishes, and ganoid fishes. Common invertebrates of the Devonian were crinoids, starfishes, sponges, and early ammonites; trilobites and graptolites became scarcer. An unusual surge of coral reef growth also occurred and corals were never again as prolific. Of land animals, the chief vestige is the footprint of a primitive salamanderlike amphibian in the Upper Devonian of Pennsylvania. Trees made their first appearance; the Devonian plants were the earliest to be extensively preserved as fossils, but their high degree of development suggests that more primitive forms existed earlier.

Author not available, DEVONIAN PERIOD., The Columbia Encyclopedia, Sixth Edition 2008

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The Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press