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	Devonian period stages Stages in the Devonian period
	The Devonian period (419-359 mya), originally named for fossils and rock formations found in Devonshire in southern England, was defined by Roderick Murchison and Adam Sedwick between 1830-1840. They identified the Devonian period with red and brown oxidized sedimentary deposits known as the Old Red Sandstone. The Early Devonian period comprises the Lochkovian, Praghian and Emsian stages (417-391 mya). The Middle Devonian period includes the Eifellian and Givetian stages (391-370 mya),  and the Late Devonian is divided into the Frasnian and Famennian stages (370-354 mya). The Devonian period saw major shifting of continental plates related to undersea tectonic and volcanic action. Convergence of the continents of North American and Baltica in the Early Devonian created the continent called Laurasia, which contained large zones of arid, near desert conditions. This is the source of the Old Red Sandstone beds, which contain hematite, typical of drought conditions. Collision of continental plates also caused the Taconic and Caledonian orgenies, resulting in the uplift of the northern Appalachian mountains of New York state and Canada, and the Caledonian mountains in the British Isles and Scandanavia. By the Permian period, Laurasia and Gondwana would merge into the supercontinent Pangaea. High sea levels prevailed during the Devonian, often called the "Age of Fishes." This was a time of major developments of aquatic groups, as well as terrestial plants. Among vertebrates many branches of jawed fish (gnathostomes) expanded. Armored fish called placoderms were numerous during the lower stages of the Devonian period, but became extinct in the Late Devonian. The first appearance of tetrapods occurred in the Late Devonian period, when a group of early tetrapods derived from lobe-finned fish first colonized the shorelines between 380 and 360 mya. This was preceded by a branching of bony fishes (Ostyichthyes) into two main orders, ray-finned fishes (actinopterygians) and lobe-finned fishes (sarcopterygians).  The pectoral fins of the latter  were modified into a pair of long, arthropod-like limbs which had elbow-like joints, leading to evolution of fish-like tetrapods who were the direct ancestors of amphibians.             References Clack, Jennifer 2012. Gaining Ground .
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