Jurassic
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{{Geological period
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[[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}} 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]]'''
|
|-
| [[Tithonian]]
| ({{period start|tithonian}} ± 4.0 – 145.5 ± 4.0 [[annum|Ma]])
|-
| [[Kimmeridgian]]
| (155.7 ± 4.0 – 150.8 ± 4.0 Ma)
|-
| [[Oxfordian stage|Oxfordian]]
| (161.2 ± 4.0 – 155.7 ± 4.0 Ma)
|-
| '''[[Middle Jurassic]]'''
|
|-
| [[Callovian]]
| (164.7 ± 4.0 – 161.2 ± 4.0 Ma)
|-
| [[Bathonian]]
| (167.7 ± 3.5 – 164.7 ± 4.0 Ma)
|-
| [[Bajocian]]
| (171.6 ± 3.0 – 167.7 ± 3.5 Ma)
|-
| [[Aalenian]]
| (175.6 ± 2.0 – 171.6 ± 3.0 Ma)
|-
| '''[[Early Jurassic|Lower/Early Jurassic]]'''
|
|-
| [[Toarcian]]
| (183.0 ± 1.5 – 175.6 ± 2.0 Ma)
|-
| [[Pliensbachian]]
| (189.6 ± 1.5 – 183.0 ± 1.5 Ma)
|-
| [[Sinemurian]]
| (196.5 ± 1.0 – 189.6 ± 1.5 Ma)
|-
| [[Hettangian]]
| (199.6 ± 0.6 – 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 — ''[[Camarasaurus]]'', ''[[Apatosaurus]]'', ''[[Diplodocus]]'', ''[[Brachiosaurus]]'', and many others—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]]