Jurassic 15655 225317144 2008-07-13T01:42:56Z UnitedStatesian 3461395 clarified {{Geological period |image=LateJurassicGlobal.jpg |o2=26 |co2=1950 |temp=16.5 }} [[Image:Europasaurus holgeri Scene 2.jpg|thumb|right|280px|Large dinosaurs were dominant during the Jurassic Period.]] The '''Jurassic''' is a [[geologic period|geologic period and system]] that extends from about {{period start}}{{period start error}} [[annum|Ma]] (million years ago) to {{period end}}{{period end error}}&nbsp;Ma, that is, from the end of the [[Triassic]] to the beginning of the [[Cretaceous]]. The Jurassic constitutes the middle period of the [[Mesozoic]] era, also known as the "Age of Reptiles". The start of the period is marked by the major [[Triassic-Jurassic extinction event]]. The start and end of the period are defined by carefully selected locations; the uncertainty in dating arises from trying to date these horizons. The Jurassic was named by [[Alexandre Brongniart]] for the extensive marine [[limestone]] exposures of the [[Jura Mountains]], in the region where [[Germany]], [[France]] and [[Switzerland]] meet. == Divisions == The Jurassic period of time is usually broken into [[Early Jurassic|Early]], [[Middle Jurassic|Middle]], and [[Late Jurassic]] subdivisions, also known as ''Lias'', ''Dogger'' and ''Malm''. The corresponding terms for the rocks are Lower, Middle, and Upper Jurassic. The [[faunal stage]]s from youngest to oldest are: {| | '''[[Late Jurassic|Upper/Late Jurassic]]''' | |- |&nbsp; [[Tithonian]] | ({{period start|tithonian}} ± 4.0 &ndash; 145.5 ± 4.0 [[annum|Ma]]) |- |&nbsp; [[Kimmeridgian]] | (155.7 ± 4.0 &ndash; 150.8 ± 4.0 Ma) |- |&nbsp; [[Oxfordian stage|Oxfordian]] | (161.2 ± 4.0 &ndash; 155.7 ± 4.0 Ma) |- | '''[[Middle Jurassic]]''' | |- |&nbsp; [[Callovian]] | (164.7 ± 4.0 &ndash; 161.2 ± 4.0 Ma) |- |&nbsp; [[Bathonian]] | (167.7 ± 3.5 &ndash; 164.7 ± 4.0 Ma) |- |&nbsp; [[Bajocian]] | (171.6 ± 3.0 &ndash; 167.7 ± 3.5 Ma) |- |&nbsp; [[Aalenian]] | (175.6 ± 2.0 &ndash; 171.6 ± 3.0 Ma) |- | '''[[Early Jurassic|Lower/Early Jurassic]]''' | |- |&nbsp; [[Toarcian]] | (183.0 ± 1.5 &ndash; 175.6 ± 2.0 Ma) |- |&nbsp; [[Pliensbachian]] | (189.6 ± 1.5 &ndash; 183.0 ± 1.5 Ma) |- |&nbsp; [[Sinemurian]] | (196.5 ± 1.0 &ndash; 189.6 ± 1.5 Ma) |- |&nbsp; [[Hettangian]] | (199.6 ± 0.6 &ndash; 196.5 ± 1.0 Ma) |} == Paleogeography == [[Image:MakhteshGadolCenter02.jpg|thumb|left|250px|Jurassic limestones and marls (the Matmor Formation) in southern [[Israel]].]] During the early Jurassic, the [[supercontinent]] [[Pangaea]] broke up into the northern supercontinent [[Laurasia]] and the southern supercontinent [[Gondwana]]; the [[Gulf of Mexico]] opened in the new rift between North America and what is now Mexico's [[Yucatan Peninsula]]. The Jurassic North [[Atlantic Ocean]] was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart.<ref>[http://www.scotese.com/late1.htm Late Jurassic<!-- Bot generated title -->]</ref> The [[Tethys Ocean|Tethys Sea]] closed, and the [[Mediterranean Basin|Neotethys]] basin appeared. Climates were warm, with no evidence of [[glacier|glaciation]]. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed. The Jurassic geological record is good in western [[Europe]], where extensive marine sequences indicate a time when much of the continent was submerged under shallow tropical seas; famous locales include the [[Jurassic Coast]] [[World Heritage Site]] and the renowned late Jurassic ''[[lagerstätte]]n'' of [[Holzmaden]] and [[Solnhofen limestone|Solnhofen]].<ref>[http://www.urweltmuseum.de/Englisch/museum_eng/Geologie_eng/Tektonik_eng.htm Jurassic Period<!-- Bot generated title -->]</ref> In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface.<ref>http://www.nationalatlas.gov/articles/geology/legend/ages/jurassic.html map]</ref> Though the [[Epeiric Sea|epicontinental]] [[Sundance Sea]] left marine deposits in parts of the northern plains of the [[United States]] and [[Canada]] during the late Jurassic, most exposed sediments from this period are continental, such as the [[alluvium|alluvial]] deposits of the [[Morrison Formation]]. The Jurassic was a time of [[calcite sea]] geochemistry in which low-magnesium [[calcite]] was the primary inorganic marine precipitate of calcium carbonate. [[Carbonate hardgrounds]] were thus very common, along with calcitic [[ooids]], calcitic cements, and invertebrate faunas with dominantly calcitic skeletons (Stanley and Hardie, 1998, 1999). The first of several massive [[batholith]]s were emplaced in the northern [[American cordillera|Cordillera]] beginning in the mid-Jurassic, marking the [[Nevadan orogeny]].<ref>Monroe and Wicander, 607.</ref> Important Jurassic exposures are also found in [[Russia]], [[India]], [[South America]], [[Japan]], [[Australasia]], and the [[United Kingdom]]. == Fauna == [[Image:Fischsaurier fg01.jpg|thumb|A reptile named ''Ichthyosaurus'' from Liassic oil slates in Holzmaden, southern [[Germany]].]] [[Image:JurassicMarineIsrael.JPG|thumb|[[Gastropod]] and attached mytilid [[bivalve]]s on a Jurassic limestone bedding plane in southern [[Israel]].]] ===Aquatic and marine=== During the Jurassic, the primary vertebrates living in the seas were [[fish]] and marine [[reptile]]s. The latter include [[ichthyosaur]]s, [[plesiosauria|plesiosaurs]] and marine [[crocodilia|crocodiles]], of the families [[Teleosauridae]] and [[Metriorhynchidae]]. In the [[invertebrate]] world, several new groups appeared, including [[rudists]] (a [[reef]]-forming variety of [[bivalvia|bivalves]]) and [[belemnites]]. The Jurassic also had diverse encrusting and boring (sclerobiont) communities (see Taylor & Wilson, 2003), and it saw a significant rise in the [[bioerosion]] of carbonate shells and hardgrounds. Especially common is the [[ichnotaxa|ichnogenus]] ([[trace fossil]]) ''Gastrochaenolites''. === Terrestrial === On land, large [[archosaur]]ian reptiles remained dominant. The Jurassic was the golden age of the great [[sauropod]]s &mdash; ''[[Camarasaurus]]'', ''[[Apatosaurus]]'', ''[[Diplodocus]]'', ''[[Brachiosaurus]]'', and many others&mdash;that roamed the land late in the period; their mainstays were either the [[prairie]]s of [[fern]]s, palm-like [[cycad]]s and [[bennettitales]], or the higher coniferous growth, according to their adaptations. They were preyed upon by large [[theropod]]s as for example ''[[Ceratosaurus]]'', ''[[Megalosaurus]]'', ''[[Torvosaurus]]'' and ''[[Allosaurus]]''. All these belong to the 'lizard hipped' or [[saurischia]]n branch of the [[dinosaur]]s. During the Late Jurassic, the first [[Aves|birds]] [[Evolution|evolved]] from small [[coelurosaur]]ian dinosaurs. [[Ornithischia]]n dinosaurs were less predominant than saurischian dinosaurs, although some like [[stegosaur]]s and small [[ornithopod]]s played important roles as small and medium-to-large (but not sauropod-sized) herbivores. In the air, [[pterosaur]]s were common; they ruled the skies, filling many ecological roles now taken by [[bird]]s. == Flora == The arid, continental conditions characteristic of the [[Triassic]] steadily eased during the Jurassic period, especially at higher latitudes; the warm, humid climate allowed lush jungles to cover much of the landscape.<ref>Haines, 2000.</ref> [[Conifers]] dominated the flora, as during the Triassic; they were the most diverse group and constituted the majority of large trees. Extant conifer families that flourished during the Jurassic included the [[Araucariaceae]], [[Cephalotaxaceae]], [[Pinaceae]], [[Podocarpaceae]], [[Taxaceae]] and [[Taxodiaceae]].<ref>Behrensmeyer ''et al'', 1992, 349.</ref> The extinct Mesozoic conifer family [[Cheirolepidiaceae]] dominated low latitude vegetation, as did the shrubby [[Bennettitales]].<ref>Behrensmeyer ''et al.'', 1992, 352</ref> [[Cycad]]s were also common, as were [[ginkgo]]s and [[tree ferns]] in the forest. Smaller [[fern]]s were probably the dominant undergrowth. [[Caytoniacea|Caytoniaceous seed ferns]] were another group of important plants during this time and are thought to have been shrub to small-tree sized.<ref>Behrensmeyer ''et al.'', 1992, 353</ref> Ginkgo-like plants were particularly common in the mid- to high northern latitudes. In the Southern Hemisphere, [[podocarps]] were especially successful, while Ginkgos and [[Czekanowskiales]] were rare.<ref>Haines, 2000.</ref><ref>Behrensmeyer ''et al.'', 1992, 352</ref> ==Notes:== <references/> ==References== *Behrensmeyer, Anna K., Damuth, J.D., DiMichele, W.A., Potts, R., Sues, H.D. & Wing, S.L. (eds.) (1992), ''Terrestrial Ecosystems through Time: the Evolutionary Paleoecology of Terrestrial Plants and Animals'', [[University of Chicago Press]], Chicago and London, ISBN 0-226-04154-9 (cloth), ISBN 0-226-04155-7 (paper) * Haines, Tim (2000) ''Walking with Dinosaurs: A Natural History'', New York: Dorling Kindersley Publishing, Inc., p. 65. ISBN 0-563-38449-2 * Kazlev, M. Alan (2002) [http://www.palaeos.com/Mesozoic/Jurassic/Jurassic.htm Paleos website] Accessed Jan. 8, 2006 *Mader, Sylvia (2004) Biology, eighth edition *Monroe, James S., and Reed Wicander. (1997) ''The Changing Earth: Exploring Geology and Evolution'', 2nd ed. Belmont: West Publishing Company, 1997. ISBN 0-314-09577-2 * Ogg, Jim; June, 2004, ''Overview of Global Boundary Stratotype Sections and Points (GSSP's)'' http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006. *Stanley, S.M. and Hardie, L.A. (1998). "Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry". Palaeogeography, Palaeoclimatology, Palaeoecology 144: 3-19. *Stanley, S.M. and Hardie, L.A. (1999). "Hypercalcification; paleontology links plate tectonics and geochemistry to sedimentology". GSA Today 9: 1-7. * Taylor, P.D. and Wilson, M.A., 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103. [http://www.wooster.edu/geology/Taylor%26Wilson2003.pdf] ==External links== *[http://www.geo-lieven.com/erdzeitalter/jura/jura.htm Examples of Jurassic Fossils] {{Wiktionary}} {{Commonscat|Jurassic}} {{Jurassic Footer}} {{Mesozoic Footer}} [[Category:Jurassic| ]] [[ar:عصر جوراسي]] [[ast:Xurásicu]] [[br:Juraseg]] [[bg:Юра (период)]] [[ca:Juràssic]] [[cs:Jura]] [[da:Jura (geologi)]] [[de:Jura (Geologie)]] [[et:Juura (geoloogia)]] [[es:Jurásico]] [[eo:Ĵurasio]] [[fr:Jurassique]] [[gl:Xurásico]] [[ko:쥐라기]] [[hr:Jura (period)]] [[id:Jura (periode)]] [[is:Júra]] [[it:Giurassico]] [[he:יורה (גאולוגיה)]] [[ka:იურული სისტემა]] [[kk:Юра кезеңі]] [[la:Aevum Iurassicum]] [[lb:Jura (Geologie)]] [[lt:Jura]] [[hu:Jura (időszak)]] [[nl:Jura (periode)]] [[ja:ジュラ紀]] [[no:Jura (geologi)]] [[nn:Juratida]] [[pl:Jura]] [[pt:Jurássico]] [[ro:Jurasic]] [[ru:Юрский период]] [[simple:Jurassic]] [[sk:Jura (geochronologická jednotka)]] [[sl:Jura]] [[sr:Јура]] [[sh:Jura (period)]] [[fi:Jurakausi]] [[sv:Jura (period)]] [[th:ยุคจูแรสซิก]] [[vi:Kỷ Jura]] [[tr:Jura Devri]] [[uk:Юрський період]] [[zh:侏罗纪]]