Eocene 9419 226007706 2008-07-16T12:29:17Z Morbas 1187917 /* Grande Coupure */ {{TOCright}} The '''Eocene [[Geologic time scale|epoch]]''' (55.8 ± 0.2 - 33.9 ± 0.1 [[annum|Ma]]) is a major division of the [[geologic timescale]] and the second epoch of the [[Palaeogene]] period in the [[Cenozoic]] era. The Eocene spans the time from the end of the [[Paleocene]] epoch to the beginning of the [[Oligocene]] epoch. The start of the Eocene is marked by the emergence of the first modern [[mammal]]s. The end is set at a major [[extinction event]] called '''[[#Grande Coupure|Grande Coupure]]''' (the "Great Break" in continuity), which may be related to the impact of one or more large [[Meteoroid#Bolide|bolides]] in [[Popigai crater|Siberia]] and in what is now [[Chesapeake Bay impact crater|Chesapeake Bay]]. As with other [[geologic period]]s, the [[Stratum|strata]] that define the start and end of the epoch are well identified,<ref>The extinction of the Hantkeninidae, a planktonic family of [[foraminifera]] became became generally accepted as marking the Eocene-Oligocene boundary; in 1998 [[Massignano]] in [[Umbria]], central Italy, was designated the [[Global Boundary Stratotype Section and Point]] (GSSP).</ref> though their exact dates are slightly uncertain. The name Eocene comes from the [[Ancient Greek|Greek]] {{polytonic|ἠώς}} (''eos'', [[dawn]]) and {{polytonic|καινός}} (''kainos'', new) and refers to the "dawn" of modern ('new') mammalian [[fauna]] that appeared during the epoch. {{Paleogene Footer}} ==Subdivisions== The Eocene epoch is usually broken into Early and Late, or - more usually - Early, Middle, and Late subdivisions. The corresponding [[rocks]] are referred to as Lower, Middle, and Upper Eocene. The [[Faunal stage]]s from youngest to oldest are: {| | [[Priabonian]] | (37.2 ± 0.1 – 33.9 ± 0.1 Ma) |- | [[Bartonian]] | (40.4 ± 0.2 – 37.2 ± 0.1 Ma) |- | [[Lutetian]] | (48.6 ± 0.2 – 40.4 ± 0.2 Ma) |- | [[Ypresian]] | (55.8 ± 0.2 – 48.6 ± 0.2 Ma) |} The Ypresian and occasionally the Lutetian constitute the Lower, the Priabonian and sometimes the Bartonian the Upper subsection; alternatively, the Lutetian and Bartonian are united as the Middle Eocene. ==Climate== Marking the start of the Eocene, [[Earth]] heated up in one of the most rapid (in geologic terms) and extreme [[global warming]] events recorded in geologic history, called the [[Paleocene-Eocene Thermal Maximum]] or Initial Eocene Thermal Maximum (PETM or IETM). This was an episode of rapid and intense warming (up to 7[[°C]] at high [[latitude]]s) that lasted less than 100,000 years <ref>[http://www.giss.nasa.gov/research/briefs/schmidt_02/ NASA GISS: Science Briefs: Ocean Burps and Climate Change?<!-- Bot generated title -->]</ref>. The Thermal Maximum provoked a sharp extinction event that distinguishes [[Eocene fauna]] from the [[ecosystem]]s of the Paleocene. The Eocene global [[climate]] was perhaps the most homogeneous of the Cenozoic; the temperature gradient from [[equator]] to [[Geographical pole|pole]] was only half that of today's, and deep [[ocean current]]s were exceptionally warm.<ref>http://www.ga.gov.au/odp/publications/tnotes/tn20-4/leg171c.html</ref> The [[polar regions]] were much warmer than today, perhaps as mild as the modern-day [[Pacific Northwest]]; [[temperate forest]]s extended right to the poles, while rainy [[tropical]] climates extended as far north as 45°. The difference was greatest in the temperate latitudes; the climate in the tropics however, was probably similar to today's.<ref>Stanley, 508</ref> Climates remained warm through the rest of the Eocene, although slow [[global cooling]] triggered by the [[Azolla event]], which eventually led to the Pleistocene [[glaciation]]s, started as ocean currents around [[Antarctica]] formed.{{misleading}} ==Paleogeography== During the Eocene, the [[continent]]s continued to [[plate tectonics|drift]] toward their present positions. At the beginning of the period, [[Australia]] and Antarctica remained connected, and warm equatorial currents mixed with colder Antarctic waters, distributing the [[heat]] around the [[planet]] and keeping global temperatures high. But when Australia split from the southern continent around 45 mya, the warm equatorial currents were deflected away from Antarctica, and an isolated cold water channel developed between the two continents. The Antarctic region cooled down, and the ocean surrounding Antarctica began to freeze, sending cold water and [[icefloe]]s north, reinforcing the cooling. The northern [[supercontinent]] of [[Laurasia]] began to break up, as [[Europe]], [[Greenland]] and [[North America]] drifted apart. In western North America, [[Orogeny|mountain building]] started in the Eocene, and huge lakes formed in the high flat basins among uplifts, resulting in the deposition of the [[Green River Formation]] [[lagerstätte]]. In Europe, the [[Tethys Sea]] finally vanished, while the uplift of the [[Alps]] isolated its final remnant, the [[Mediterranean Sea|Mediterranean]], and created another shallow sea with island [[archipelago]]s to the north. Though the North [[Atlantic Ocean|Atlantic]] was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar. [[India]] continued its journey away from [[Africa]] and began its collision with [[Asia]], [[folding]] the [[Himalaya]]s into existence. It is hypothesized that the Eocene hothouse world was caused by runaway global warming from released [[methane clathrate]]s deep in the [[ocean]]s. The [[clathrate]]s were buried beneath [[mud]] that was disturbed as the oceans warmed. [[Methane]] ([[Carbon|C]][[Hydrogen|H]]<sub>4</sub>) has ten to twenty times the [[greenhouse gas]] effect of [[carbon dioxide]] (C[[Oxygen|O]]<sub>2</sub>). ==Flora== At the beginning of the Eocene, the high [[temperature]]s and warm oceans created a moist, balmy environment, with [[forest]]s spreading throughout the Earth from pole to pole. Apart from the driest [[desert]]s, Earth must have been entirely covered in forests. Polar forests were quite extensive. [[Fossil]]s and even preserved remains of trees such as [[swamp cypress]] and [[dawn redwood]] from the Eocene have been found on [[Ellesmere Island]] in the [[Arctic]]. The preserved remains are not fossils, but actual pieces preserved in oxygen-poor [[water]] in the [[swamp]]y forests of the time and then buried before they had the chance to [[decompose]]. Even at that time, Ellesmere Island was only a few degrees in latitude further south than it is today. Fossils of [[subtropical]] and even tropical trees and plants from the Eocene have also been found in Greenland and [[Alaska]]. [[Tropical rainforest]]s grew as far north as the Pacific Northwest and Europe. [[Palm tree]]s were growing as far north as Alaska and northern Europe during the early Eocene, although they became less abundant as the climate cooled. Dawn redwoods were far more extensive as well. Cooling began mid-period, and by the end of the Eocene continental interiors had begun to dry out, with forests thinning out considerably in some areas. The newly-evolved [[grasses]] were still confined to [[river]] banks and [[lake]] shores, and had not yet expanded into [[plain]]s and [[savanna]]s. The cooling also brought [[season]]al changes. [[Deciduous]] trees, better able to cope with large temperature changes, began to overtake [[evergreen]] tropical species. By the end of the period, deciduous forests covered large parts of the northern continents, including North America, [[Eurasia]] and the Arctic, and rainforests held on only in equatorial [[South America]], [[Africa]], [[India]] and Australia. Antarctica, which began the Eocene fringed with a warm temperate to sub-tropical rainforest, became much colder as the period progressed; the heat-loving tropical [[flora (plants)|flora]] was wiped out, and by the beginning of the Oligocene, the continent hosted deciduous forests and vast stretches of [[tundra]]. ==Fauna== [[Image:Mesonyx.jpg|thumb|right|''[[Mesonyx]]'', a [[carnivorous]] [[ungulate]]]] [[Image:Nummulitids.jpg|thumb|right|Fossil nummulitid [[foraminifera]]ns showing microspheric and megalospheric individuals; Eocene of the [[United Arab Emirates]]; scale in mm.]] The oldest known [[fossil]]s of most of the modern mammal orders appear within a brief period during the early Eocene. At the beginning of the Eocene, several new mammal groups arrived in North America. These modern mammals, like [[artiodactyl]]s, [[perissodactyls]] and [[primate]]s, had features like long, thin [[leg]]s, [[Foot|feet]] and [[hand]]s capable of grasping, as well as differentiated [[teeth]] adapted for chewing. [[Dwarf]] forms reigned. All the members of the new mammal orders were small, under 10&nbsp;[[kg]]; based on comparisons of tooth size, Eocene mammals were only 60% of the size of the primitive Paleocene mammals that preceded them. They were also smaller than the mammals that followed them. It is assumed that the hot Eocene temperatures favored smaller animals that were better able to manage the heat. Both groups of modern [[ungulate]]s (hoofed animals) became prevalent because of a major radiation between Europe and North America; along with carnivourous ungulates like ''[[Mesonyx]]''. Early forms of many other modern mammalian orders appeared, including [[bat]]s, [[proboscidea|proboscidian]]s, primates, [[rodent]]s and [[marsupials]]. Older primitive forms of mammals declined in variety and importance. Important Eocene land fauna fossil remains have been found in western North America, Europe, [[Patagonia]], [[Egypt]] and [[southeast Asia]]. Marine fauna are best known from [[South Asia]] and the [[southeast United States]]. Reptile fossils from this time, such as fossils of [[python]]s and [[turtle]]s, are abundant. During the Eocene, plants and marine faunas became quite modern. Many modern [[Aves|bird]] orders first appeared in the Eocene. Some [[scientist]]s believed that the first primates appeared around 55 Ma in the Ypresian era of the Eocene; however, the [[molecular clock]] and new [[paleontological]] finds indicate that the first primates appeared much earlier, around 90 Ma in the [[Cretaceous]] era.{{Fact|date=January 2008}} ===Oceans=== [[Image:Basilosaurus_BW.jpg|thumb|right|150px|''Basilosaurus'']] [[Image:Prorastomus_BW.jpg|thumb|left|150px|''[[Prorastomus]]'', an early [[sirenian]]]] The Eocene oceans were warm and teeming with [[fish]] and other sea life. The first [[Carcharhiniformes|Carcharinid sharks]] appeared, as did early marine mammals, including ''[[Basilosaurus]]'', an early species of [[whale]] that is thought to be descended from land animals that existed earlier in the Eocene, the [[hoof]]ed [[predator]]s called [[mesonychid]]s, of which ''[[Mesonyx]]'' was a member. The first [[sirenian]]s, relatives of the [[elephant]]s, also appeared at this time. ==''Grande Coupure''== [[Image:Extinction Intensity.svg|thumb|275px|right|The "end Eocene" event.]] The ''Grande Coupure'', or "great break" in continuity,<ref> also termed the MP 21 event.</ref> with a major European turnover in mammalian fauna about 33.5 Ma, marks the end of the last phase of Eocene assemblages, the [[Priabonian]], and the arrival in Europe of Asian immigrants. The Grande Coupure is characterized by widespread extinctions and [[allopatric speciation]] in small isolated [[Relict|relict population]]s.<ref>Called "dispersal-generated origination" in Hooker et al. 2004</ref> It was given its name in 1910 by the [[Switzerland|Swiss]] palaeontologist [[Hans Georg Stehlin]],<ref>H.G. Stehlen, 1910. "Remarques sur les faunules de Mammifères des couches eocenes et oligocenes du Bassin de Paris," in ''Bulletin de la Société Géologique de France,'' '''4''''.9, pp 488-520.</ref> to characterise the dramatic turnover of European mammalian fauna, which he placed at the Eocene-Oligocene boundary. A comparable turnover in Asian fauna has since been called the "Mongolian Remodelling". The Grande Coupure marks a break between [[Endemism|endemic]] European faunas before the break and mixed faunas with a strong Asian component afterwards. [[J.J. Hooker]] and his team summarized the break: :"Pre-Grande Coupure faunas are dominated by the perissodact family [[Palaeotheriidae]] (distant [[horse]] relatives), six families of artiodactyls (cloven-hoofed mammals) (Anoplotheriidae, Xiphodontidae, Choeropotamidae, Cebochoeridae, Dichobunidae and Amphimerycidae), the rodent family Pseudosciuridae, the primate families Omomyidae and Adapidae, and the [[archontan]] family Nyctitheriidae. :"Post-Grande Coupure faunas include the true [[rhino]]s (family Rhinocerotidae), three artiodactyl families (Entelodontidae, Anthracotheriidae and Gelocidae) related respectively to [[pig]]s, [[Hippopotamus|hippo]]s and [[ruminant]]s, the [[rodent]] families Eomyidae, Cricetidae ([[hamster]]s) and Castoridae ([[beaver]]s), and the lipotyphlan family Erinaceidae ([[hedgehog]]s). The speciose genus Palaeotherium plus ''[[Anoplotherium]]'' and the families Xiphodontidae and Amphimerycidae were observed to disappear completely. :"Only the [[marsupial]] family [[Herpetotheriidae]], the artiodactyl family [[Cainotheriidae]], and the rodent families [[Theridomyidae]] and Gliridae ([[dormice]]) crossed the faunal divide undiminished." (Hooker et al. 2004) Whether this abrupt change was caused by [[climate change]] associated with the earliest polar glaciations<ref>A major cooling event preceded the Grande Coupure, based on pollen studies in the Paris Basin conducted by Chateauneuf ([[J.J. Chateauneuf]], 1980. "Palynostratigraphie et paleoclimatologie de l'Éocene superieur et de l'Oligocene du Bassin de [[Paris]] ([[France]])" in ''Mémoires du Bureau de Recherches Géologiques et Minières'', '''116''' 1980).</ref> and a major fall in sea levels, or by competition with taxa dispersing from Asia, few argue for an [[Oligocene#Climate|isolated single cause]]. More spectacular causes are related to the impact of one or more large bolides in Siberia and in the Chesapeake Bay impact crater. Improved correlation of [[northwest Europe]]an successions to global events (Hooker et al. 2004) confirms the Grande Coupure as occurring in the earliest Oligocene, with a hiatus of about 350 [[millennia]] prior to the first record of post-Grande Coupure Asian immigrant taxa. An element of the paradigm of the Grande Coupure was the apparent [[extinction]] of all European primates at the Coupure: the recent discovery<ref>Meike Kohler and Salvador Moya-Sola, "A finding of Oligocene primates on the European continent," in ''Proceedings of the National Academy of Sciences of the United States'' ''' 96'''.25 (Dec. 7, 1999), pp 14664-14667</ref> of a [[mouse]]-sized early Oligocene [[omomyid]], reflecting the better survival chances of small mammals, further undercut the Grand Coupure [[paradigm]]. ==See also== * [[Green River Formation]] in western North America * [[List of fossil sites]] ''(with link directory)'' * [[London Clay]] * [[Messel Pit]] in Germany ==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. *Stanley, Steven M. ''Earth System History.'' [[New York]]: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 *J.J. Hooker M.E. Collinson and N.P. Sille, 2004. "Eocene–Oligocene mammalian faunal turnover in the [[Hampshire Basin]], [[England]]: calibration to the global time scale and the major cooling event" in ''Journal of the Geological Society'' '''161'''.2, pp 161-172 ([http://www.findarticles.com/p/articles/mi_qa3721/is_200403/ai_n9392785 on-line text]) ==External links== {{Commonscat|Eocene}} *[http://www.scotese.com/ PaleoMap Project] *[http://www.palaeos.com/Cenozoic/Eocene/Eocene.htm Paleos Eocene page] *[http://www.pbs.org/wgbh/evolution/change/deeptime/eocene.html PBS Deep Time: Eocene] *[http://www.coloradomtn.edu/campus_rfl/staff_rfl/kohls/eocene.html Eocene Fossils] *[http://www.dmap.co.uk/fossils/ Eocene and Oligocene Fossils] *[http://www.carnegiemnh.org/research/eosimias/index.html Eocene Primate, Carnegie Museum of Natural History] *[http://www.sas.upenn.edu/earth/arctic/ The UPenn Fossil Forest Project, focusing on the Eocene polar forests in Ellesmere Island, Canada] *[http://www.intersurf.com/~chalcedony/Basilosaurus1.html Basilosaurus Primitive Eocene Whales] *[http://darla.neoucom.edu/DEPTS/ANAT/whaleorigins.htm Eocene Whale Origins] *[http://jan.ucc.nau.edu/~rcb7/terpaleo.html Detailed maps of Tertiary Western North America] *[http://www.scotese.com/newpage9.htm Map of Eocene Earth] [[Category:Eocene| ]] {{link FA|ca}} {{link FA|es}} [[ang:Eocene]] [[ast:Eocenu]] [[br:Eosen]] [[ca:Eocè]] [[cs:Eocén]] [[da:Eocæn]] [[de:Eozän]] [[et:Eotseen]] [[es:Eoceno]] [[eo:Eoceno]] [[fr:Éocène]] [[ko:에오세]] [[id:Eosen]] [[it:Eocene]] [[he:איאוקן]] [[lb:Eozän]] [[hu:Eocén]] [[nl:Eoceen]] [[ja:始新世]] [[no:Eocen]] [[nn:Eocen]] [[nds:Eozän]] [[pl:Eocen]] [[pt:Eoceno]] [[ro:Eocen]] [[sk:Eocén]] [[sh:Eocen]] [[fi:Eoseenikausi]] [[sv:Eocen]] [[vi:Thế Eocen]] [[uk:Еоценова епоха]] [[zh:始新世]]