Devonian 7992 222332287 2008-06-28T19:45:14Z Quadell 57108 Converting [1] to <ref>, and/or misc fixes using [[Project:AutoWikiBrowser|AWB]] {{dablink|For the Celtic language, see [[Southwestern Brythonic language]]; for the residents of the English county, see [[Devon]].}} {{Geological period |from=416 |middle=384 |to=359 |error-from=2.8 |error-to=2.5 |image=LateDevonianGlobal.jpg |o2=15 |co2=2200 |temp=20 }} The '''Devonian''' is a [[geologic period|geologic period and system]] of the [[Paleozoic]] era spanning from {{Ma|416|&plusmn;2.8}} to {{Ma|359.2|&plusmn;2.5}}&nbsp;million years ago {{ICS 2004}}. It is named after [[Devon]], [[England]], where rocks from this period were first studied. During the Devonian Period, which occurred in the Paleozoic era, the first [[fish]] evolved [[Leg (anatomy)|legs]]<ref>See ''[[Tiktaalik]]''.</ref>and started to walk on [[Landform|land]] as [[tetrapod]]s around 365 [[Mega-annum|Ma]]. Various terrestrial arthropods also became well-established.<!--Arthropods had been on the land since the Silu/Ordovican. See Tumblagooda sandstone.--> The first [[Spermatophyte|seed-bearing plants]] spread across dry land, forming huge [[forest]]s. In the [[ocean]]s, primitive [[shark]]s became more numerous than in the [[Silurian]] and the [[late Ordovician]], and the first [[Sarcopterygii|lobe-finned]] and [[bony fish]]. The first [[ammonite]] [[mollusk]]s appeared, and [[trilobite]]s, the mollusc-like [[brachiopod]]s, as well as great [[coral reef]]s were still common. The [[Late Devonian extinction]] severely affected marine life. The [[paleogeography]] was dominated by the [[supercontinent]] of [[Gondwana]] to the south, the [[continent]] of [[Siberia (continent)|Siberia]] to the north, and the early formation of the small supercontinent of [[Euramerica]] in the middle. == Naming == [[Image:Devonianscene.jpg|thumb|left|275px|The Devonian period marks the beginning of extensive land colonization by [[plant]]s. With large [[herbivorous]] land-animals not yet being present, large forests could grow and shape the landscape.]] The period is named after [[Devon]], a county in southwestern England, where Devonian outcrops are common. While the [[stratum|rock bed]]s that define the start and end of the period are well identified, the exact dates are uncertain. According to the [[International Commission on Stratigraphy]] ([[#References|Ogg, 2004]]), the Devonian extends from the end of the [[Silurian]] Period 416.0 ± 2.8 [[million years ago]] (Mya), to the beginning of the [[Carboniferous]] Period 359.2 ± 2.5 Mya (in [[North America]], the beginning of the [[Mississippian]] subperiod of the Carboniferous) (ICS 2004). Well into the 20th century, the Devonian was often quoted as being "the age of fishes", referring to the great diversification of various piscine groups in the period. While the development of fishes is of great importance from an anthropocentric point of view (inasmuch as they are our [[vertebrate]] relatives), the name is now avoided, as fishes were but one of several important groups to see extensive development on the Devonian (see under ''[[Devonian#Devonian_biota|Devonian biota]]''). The name is frequently found in older (and a few newer) works. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the [[Old Red Sandstone]] in which early fossil discoveries were found. The Devonian has also erroneously been characterized as a "greenhouse age", due to [[sampling bias]]: most of the early Devonian-age discoveries came from the [[stratum|strata]] of [[western Europe]] and eastern [[North America]], which at the time straddled the [[Equator]] as part of the supercontinent of Euramerica where [[fossil]] signatures of widespread reefs indicate tropical [[climate]]s that were warm and moderately humid but in fact the climate in the Devonian differed greatly between [[Geologic time scale|epoch]]s and geographic regions. For example, during the [[Early Devonian]], arid conditions were prevalent through much of the world including Siberia, Australia, North America, and China, but Africa and [[South America]] had a warm [[temperate climate]]. In the [[Late Devonian]], by contrast, arid conditions were less prevalent across the world and [[temperate]] climates were more common. == Devonian subdivisions == The Devonian Period is formally broken into Early, Middle, and Late subdivisions. The rocks corresponding to these [[epoch]]s are referred to as belonging to the Lower, Middle, and Upper parts of the Devonian System. The international standard [[faunal stage]]s from youngest to oldest are: === Late (most recent) === *[[Famennian]] *[[Frasnian]] === Middle === *[[Givetian]] *[[Eifelian]] === Early (oldest) === *[[Emsian]] *[[Pragian]] *[[Lochkovian]] == Devonian palaeogeography == [[Image:380 Ma plate tectonic reconstruction.png|thumb|right|230px|Geography of the Devonian world]] The Devonian period was a time of great [[Plate tectonics|tectonic]] activity, as [[Laurasia]] and [[Gondwana]]land drew closer together. <!-- Unsourced image removed: [[Image:Early devonian earth.jpg|thumb|right|300px|Earth in [[Early Devonian]].]] --> The continent [[Euramerica]] (or Laurussia) was created in the early Devonian by the collision of [[Laurentia]] and [[Baltica]], which rotated into the natural dry zone along the [[Tropic of Capricorn]], which is formed as much in Paleozoic times as nowadays by the convergence of two great airmasses, the [[Hadley cell]] and the [[Ferrel cell]]. In these near-deserts, the [[Old Red Sandstone]] sedimentary beds formed, made red by the oxidized iron ([[hematite]]) characteristic of drought conditions. Near the [[equator]], [[Pangaea]] began to consolidate from the [[Tectonic plates|plate]]s containing [[North America]] and [[Europe]], further raising the northern [[Appalachian Mountains]] and forming the [[Caledonian orogeny|Caledonian Mountains]] in [[Great Britain]] and [[Scandinavia]]. The west coast of Devonian North America, by contrast, was a passive margin with deep silty embayments, river deltas and estuaries, in today's [[Idaho]] and [[Nevada]]; an approaching volcanic [[island arc]] reached the steep slope of the continental shelf in Late Devonian times and began to uplift deep water deposits, a collision that was the prelude to the mountain-building episode of Mississippian times called the [[Antler orogeny]]<ref>http://jan.ucc.nau.edu/~rcb7/devpaleo.html</ref>. The southern [[continent]]s remained tied together in the [[supercontinent]] of Gondwana. The remainder of modern Eurasia lay in the Northern Hemisphere. Sea levels were high worldwide, and much of the land lay submerged under shallow seas, where tropical [[reef]] organisms lived. The deep, enormous [[Panthalassa]] (the "universal ocean") covered the rest of the [[planet]]. Other minor oceans were [[Paleo-Tethys]], [[Proto-Tethys]], [[Rheic Ocean]], and [[Ural Ocean]] (which was closed during the collision with [[Siberia (continent)|Siberia]] and Baltica). Devonian rocks are oil and gas producers in some areas. == Devonian biota == [[Image:Devonianfishes ntm 1905 smit 1929.gif|thumb|right|''Devonian fishes'', from Joseph Smits "from Nebula to Man", 1905, showing early [[shark]], [[ray-finned fish]]es, a [[lungfish]] and the [[placoderm]] ''[[Bothriolepis]]''.]] [[Image:Trilobite Ductina.jpg|thumb|Fossil trilobite ''Ductina vietnamica'' from the Devonian of China]] [[Image:HederelloidSEM.jpg|thumb|SEM image of a [[hederellid|hederelloid]] from the Devonian of Michigan (largest tube diameter is 0.75 mm).]] [[Image:HederellaOH3.jpg|thumb|A Devonian spiriferid [[brachiopod]] from [[Ohio]] which served as a host substrate for a colony of [[hederellid|hederelloid]]s. The specimen is 5 cm wide.]] === Marine biota === Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by [[bryozoa]], diverse and abundant [[brachiopoda|brachiopods]], the enigmatic [[hederellid|hederelloids]], and [[coral]]s. Lily-like [[crinoids]] were abundant, and [[trilobites]] were still fairly common, but less diverse than in earlier periods due to the abundance of mobile swimming predators such as early sharks and predatory bony fish (Osteichthyes) such as [[Dunkleosteus]]. The [[ostracoderms]] were joined in the mid-Devonian by the first jawed fishes and were declining in diversity and were being out competed by the jawed fish in both the sea and [[fresh water]], also the great armored [[placoderms]], as well as the first sharks and [[ray-finned fish]]. The first abundant species of shark, the ''[[Cladoselache]]'', appeared in the oceans during the Devonian period. They became abundant and diverse. In the late Devonian the [[lobe-finned fish]] appeared, giving rise to the first [[tetrapods]]. The first [[Ammonite]]s also appeared during or slightly before the early devonian period around 400 million years ago.<ref>http://www.palaeos.com/Paleozoic/Devonian/Devonian.2.htm#Life</ref> A recently discovered fossil of a fish embryo attached to its mother by an umbilical cord in 380 million year old Devonian strata provides the earliest fossil evidence of vertebrates giving live birth to their young. <ref>[http://news.nationalgeographic.com/news/2008/05/080528-mother-fossil.html]</ref> === Reefs === A great barrier reef, now left high and dry in the [[Kimberley Basin]] of northwest [[Australia]], once extended a thousand kilometers, fringing a Devonian continent. Reefs in general are built by various [[carbonate]]-secreting organisms that have the ability to erect wave-resistant frameworks close to sea level. The main contributors of the Devonian reefs were unlike modern reefs, which are constructed mainly by corals and calcareous [[algae]]. They were composed of calcareous algae and coral-like [[Stromatoporoidea|stromatoporoids]], and tabulate and [[Rugosa|rugose corals]], in that order of importance. === Terrestrial biota === By the Devonian Period, life was well underway in its colonization of the land. The [[moss]] forests and [[bacterium|bacteria]]l and algal mats of the [[Silurian]] were joined early in the period by primitive rooted [[plant]]s that created the first stable [[soil]]s and harbored arthropods like [[mite]]s, [[scorpion]]s and [[myriapod]]s (although arthropods appeared on land much earlier than in the [[Early Devonian]] and the existence of fossils such as ''[[Climactichnites]]'' suggest that land arthropods may have appeared as early as the [[Cambrian]] period). [[Early Devonian]] plants did not have roots or leaves like the plants most common today, and many had no vascular tissue at all. They probably spread largely by vegetative growth, and did not grow much more than a few centimeters tall. Also the first possible fossils of [[insects]] appeared around 416 [[Mega-annum|Ma]] in the Early Devonian. By the Devonian, shrub-like forests of small, primitive plants existed: [[lycophyte]]s, sphenophytes, [[fern]]s, and progymnosperms had [[Evolution|evolved]]. Most of these plants had true roots and leaves, and many were quite tall. In the [[Late Devonian]], the tree-like ancestral fern ''[[Archaeopteris]]'' and the giant [[cladoxylopsid]] trees grew with true [[wood]]. (See also: [[lignin]].) These are the oldest known trees of the world's first forests. ''[[Prototaxites]]'' was the fruiting body of an enormous fungus that stood more than 8 meter tall. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterizes a recognizably modern world had its genesis in the Late Devonian. The development of soils and plant root systems probably led to changes in the speed and pattern of [[erosion]] and sediment deposition. The rapid evolution of a terrestrial ecosystem containing copious animals opened the way for the first [[vertebrate]]s to seek out a terrestrial living. By the end of the Devonian, early [[amphibia]]ns and arthropods were solidly established on the land. The earliest known trees, from the genus ''[[Wattieza]]'', appeared in the Late Devonian around 380 [[Mega-annum|Ma]].<ref>http://www.timesonline.co.uk/tol/news/uk/science/article1674051.ece</ref> The 'greening' of the continents acted as a [[carbon dioxide]] [[Carbon dioxide sink|sink]], and [[Earth's atmosphere|atmospheric]] levels of this [[greenhouse gas]] may have dropped. This may have cooled the climate and led to a massive [[extinction event]]. See [[Late Devonian extinction]]. ==Late Devonian extinction== [[Image:Extinction Intensity.svg|thumb|left|180px|Comparison of the three episodes of extinction in the Late Devonian ("Late D") to other mass extinction events in [[History of Earth|Earth's history]]. Data based on marine [[genus|genera]].]] {{Main|Late Devonian extinction}} A major extinction occurred at the beginning of the last phase of the Devonian period, the Famennian faunal stage, (the Frasnian-Famennian boundary), about 364 million years ago, when all the fossil agnathan fishes, save for the [[psammosteid]] [[heterostracan]]s, suddenly disappeared. A second strong pulse closed the Devonian period. The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota, more drastic than the familiar extinction event that closed the Cretaceous. The Devonian extinction crisis primarily affected the marine community, and selectively affected shallow warm-water organisms rather than cool-water organisms. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef-systems . Amongst the severely affected marine groups were the [[brachiopod]]s, trilobites, [[ammonite]]s, [[conodont]]s, and [[acritarch]]s, as well as jawless fish, and all placoderms. Land plants as well as freshwater species, such as our tetrapod ancestors, were relatively unaffected by the Late Devonian extinction event. Reasons for the late Devonian extinctions are still speculative. The [[Canadian]] [[paleontologist]] [[Digby McLaren]] suggested in 1969 that the Devonian extinction events were caused by an asteroid impact; however, little evidence supports the existence of a Devonian crater large enough. ==Notes== {{reflist}} == References == * Ogg, Jim; June, 2004, ''Overview of Global Boundary Stratotype Sections and Points (GSSP's)'' http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006. *[http://www.palaeos.com/Paleozoic/Devonian/Devonian.2.htm#Life Palaeos] == See also == * [[Geologic timescale]] * ''[[Phacops rana]]'': a Devonian trilobite. * [[List of fossil sites]] ''(with link directory)'' ==External links== {{Commonscat|Devonian}} *[http://www.devoniantimes.org/index.html The Devonian times] - an excellent and frequently updated resource focussing on the Devonian period *[http://www.ucmp.berkeley.edu/devonian/devlife.html UC Berkeley site introduces the Devonian.] *[http://www.nd.edu/~cneal/al375/Kimb_Geology.html Devonian reef system in northwest Australia.] * {{cite web | title=International Commission on Stratigraphy (ICS)| work=Geologic Time Scale 2004| url=http://www.stratigraphy.org/ | accessdate=Sept 19 | accessyear=2005}} *[[Falls of the Ohio State Park]] USA, Indiana. One of the largest exposed Devonian fossil beds in the world. * [http://www.geo-lieven.com/erdzeitalter/devon/devon.htm Examples of Devonian Fossils] {{Devonian Footer}} {{Paleozoic Footer}} [[Category:Devonian| ]] [[br:Devonian]] [[ca:Devonià]] [[cs:Devon (geologie)]] [[cy:Defonaidd]] [[da:Devon (geologi)]] [[de:Devon (Geologie)]] [[et:Devon]] [[es:Devónico]] [[eo:Devonio]] [[eu:Devoniar]] [[fr:Dévonien]] [[ko:데본기]] [[id:Devon (periode)]] [[is:Devontímabilið]] [[it:Devoniano]] [[he:דבון]] [[kk:Девон]] [[la:Aevum Devonianum]] [[lb:Devon (Geologie)]] [[lt:Devonas]] [[hu:Devon (időszak)]] [[nl:Devoon]] [[ja:デボン紀]] [[no:Devon (geologi)]] [[pl:Dewon]] [[pt:Devoniano]] [[ro:Devonian]] [[ru:Девонский период]] [[sk:Devón]] [[sl:Devon (geološka doba)]] [[sh:Devonij]] [[fi:Devonikausi]] [[sv:Devon (period)]] [[vi:Kỷ Devon]] [[tr:Devoniyen]] [[uk:Девонський період]] [[zh:泥盆纪]]