Eocene–Oligocene extinction event

As Grande Coupure is referred to in paleontology a significant faunal exchange, which at the turn of the Eocene / Oligocene (border Priabonium / Rupelium ) occurred. This incision was been accompanied by a deterioration of the climate and a large extinction of species, which a majority of the then Palaeotherien (early horses), primates ( Primates ), Creodonta ( Urraubtiere ) and other groups of animals were killed. New forms created then replaced the extinct taxa.

• 4.1 Plate tectonic causes
• 4.2 Climatic changes
• 4.3 Extraterrestrial causes

• 5.1 based dating from country mammalian faunal

History and terminology

The term Grande Coupure, French large ( A ) section 1909 coined by the Swiss palaeontologist Hans Georg Stehlin and introduced into the scientific literature. In English, the name of the Eocene - Oligocene extinction event or sometimes just MP 21 is used event (MP for Mammal Paleogene ).

Effects

The balance of the Grande Coupure in Europe is as follows:

• Approximately 60 % of the Eocene mammalian genera died at the beginning of Rupeliums from (Lower Oligocene ).
• 66 % of current during the Rupel species of mammals were not present in the Eocene ( as occurred in the Rupel 13 completely new families with 20 new genera on ).

Overall, the Grande Coupure led to an evolutionary transformation, diversification and Faunenerneuerung ( Faunenaustauch ).

Specifically, the following Faunengruppen were affected by extinction at the turn Priabon / Rupel:

Affected Faunengruppen

• Apatotheria ( shrew like) whose family Apatemyidae completely extinct.

• Anoplotherioidea
• Dacrytheroidea
• Xiphodontoidea
• The Choeropotamidae the family died out.

• About your family Arctoidea ( mustelids, seals, bears, etc.) lost the genus Cynodictis which was replaced by Amphicyonodon.

• Equidae ( horses). With them were the Palaeotheriidae ( a ancestral horses - side branch ) hit hard. It survived only a few genera such as Palaeotherium and Plagiolophus that but then for 2 million years after the Faunenschnitt also extinct.

• Isochromyidae ( croissant Related )
• Protoptychidae
• Reithroparomyidae
• Sciuravidae

• Isectolophidae
• Lophialetidae
• Lophiodontidae

New Releases Faunengruppen

New publications in the Rupel were:

• Artiodactyla with the Gelocidae
• Hypertragulidae
• Leptomerycidae

• Felidae (cat ) Eusmilus, Nimravus and Quercylurus

• Megadermatidae
• Phyllostomatidae

• Soricidae ( Soricoidea )

• Chalicotheriidae ( Ancylopoda )
• Tapiridae

• Amynodontidae with Cadurcotherium
• Hyracodontidae with Paraceratherium
• Rhinocerotidae with Epiaceratherium and Ronzotherium

• Aplodontia
• Castoroidea ( beaver ) with Steno Fiber
• Caviomorpha. All ( the limited on South America) families are likely to have resulted from an incurred at the Grande Coupure archetype.
• Cylindrodontidae
• Eutypomyidae
• Heteromyidae
• Myomorpha with Eomyidae
• Sciuroidea ( croissant ) with Palaeosciurus
• Tsaganomyidae

According to JJ Hooker and others ( 2004), the Grande Coupure is characterized in Europe by the transition from a purely endemic fauna of a mixed fauna with Asian elements. For them, the fauna from the Grande Coupure was clear from the perissodaktylen family of Palaeotheriidae, from 6 artiodaktylen families ( Amphimerycidae, Anoplotheriidae, Cebochoeridae, Choeropotamidae, Dichobunidae and Xiphodontidae ) of the rodent family of Pseudosciuridae, of the two primate families Omomyidae and Adapidae and of of very primitive insectivores family of Nyctitheriidae dominated.

The fauna after the Grande Coupure includes real rhinos ( family Rhinocerotidae ), 3 artiodaktyle families ( Anthracotheriidae, Entelodontidae and Gelocidae, precursor, respectively. Hippos, pigs and ruminants), the rodent families Castoridae ( beavers ), Cricetidae ( hamster ) and the insectivore family Eomyidae (hedgehog ).

Only the marsupial family Herpetotheriidae that artiodaktyle family Cainotheriidae and the two rodent families Theridomyidae and Gliridae were not affected by the Grande Coupure.

Geochemical trends in deep-sea sediments

Geochemical studies of benthic foraminifera from deep-sea sediments have provided the following results for the Grande Coupure:

• Most notable is a very rapid increase in the δ18O values ​​, the so-called oxygen anomaly Oi 1 This indicates a pronounced drop in temperature of the oceans at the Eocene - Oligocene boundary. A general drop in temperature had indeed already begun at the end of Ypresiums, however, the temperature drop across the Grande Coupure was strikingly with 1 ‰ δ18O PDB. Only in Chattian the temperatures stabilized again.
• From the Grande Coupure uses a very significant increase in the strontium isotope ratio 87Sr/86Sr, which continues down into Neogene. Increased strontium isotope ratios suggest an increased sediment input, which is triggered by increased orogenic activities.
• Coupled with the increase in the oxygen isotope ratio is a slight short-term increase in carbon isotope δ13C observed ( to also close to 1 ‰), which regresses during the course of the Rupel and then in Chattian drops again below the old level. This somewhat peculiar finding ( usually drop the carbon values ​​with increasing oxygen levels ) can be explained possibly by an increased biological production in the oceans.
• In sediments of the Priabons (at least) were discovered two iridium anomalies associated with meteorite impacts and possibly the general cooling trend even accelerated

Possible Causes

The possible causes for the Faunenschnitt are varied, the following options are considered:

• Plate tectonic
• Climatic changes
• Meteorite impacts

Plate tectonic causes

• Continuing north of the southern continents drift away from Antarctica.
• Opening of the North Atlantic between Greenland and Norway.
• Alpine orogenic movements ( folding and uplift of the Alps, Pyrenees, Rockies, etc.).

Climatic changes

The climatic changes are causally linked with the dynamic plate movements. So due to the drift of the southern continents North (Australia and South America) for the first time to break arms of the sea and Antarctica is isolated. This leads to the beginning of the Oligocene to the onset of the circumpolar ocean current around Antarctica. In the Northern Hemisphere, the North Atlantic opens and enables a connection to the Arctic Ocean.

These two Neukonstellationen bring together a global cooling of ocean temperatures around 5 ° C. At the same form in the Antarctic for the first time glacier caps. As a feedback effect of sea level therefore drops by about 30 meters and shelf seas run dry, including the location between Europe and Asia Turgai Street. This allowed Asian Faunengruppen to Europe einzuwändern and initiate the faunal upheavals of the Grande Coupure.

The worldwide drop in temperatures drew significant climatic changes by itself, which in turn impacted on plant and animal world. There was, for example, in Europe during the Eocene still a sub-tropical vegetation, so were able to establish extensive steppe areas from the Grande Coupure due to the cooler and drier climate at the same time. The endemic fauna of Europe saw himself thus exposed to a multiple evolutionary stress, which was caused by new Nahrungskonkurenten, worsening climate and environmental changes.

Extraterrestrial causes

As with other major faunal changes in the fossil record Extraterrestrial causes are out in the field for the Grande Coupure. Thus, for example, the meteorite crater of the Chesapeake Bay, from Toms Canyon and Popigai time pretty close (they are about 1 million years older ) at the Grande Coupure and could possibly be causally linked to the Faunenschnitt.

Age

The turning Priabon / Rupel and thus the Grande Coupure is absolutely with 33.9 ± 0.1 million years BP dated. The GSSP for this event is located in marine strata in Massignano in Italy. He is by the disappearance of planktonic foraminifera hantkeniniden defined (last occurrence of Turborotalia azulensis ). The GSSP also corresponds to the end of planktonic Foraminiferenstufe P 17 within the Nannofossilzone NP 21 and lies within the magnetic anomaly C 13r.1.

The occurrence of the first Asian faunas can be in North-West Europe in the lowermost Oligocene to 33, demonstrate five million years, that is, the Grande Coupure extended over a period of about 350 000 years ago.

Dating based on country mammalian faunal

For the Paleogene a detailed chronology was established on the basis of land mammals found associations (English country mammal ages or LMA). These fossil faunal fall for the individual continents very different, therefore every continent has its own chronological stages ( = ALMA Asia, Europe = ELMA, North America and South America = NALMA = SALMA ).

In Europe, the Grande Coupure is located between the stages Headonium and Suevium or between stages MP 20 and MP 21, characterized by the last occurrence ( engl. load appearance date or LAD) of Xiphodontidae and shortly thereafter the Amphimerycidae and of Palaeotherium; first appeared (English first appearance or FAD) the Castoridae, Cricetidae, Entelodon and Rhinocerotidae.

In Asia, the Grande Coupure is called the Mongolian revolution (English Mongolian Revolution), which took place between the stages Ergilium and Shandgolium. In North America, the Grande Coupure is located between the stages Chadronium and Orellum, marked by the last occurrence of Brontotheriidae, Cylindrodontidae and Oromerycidae and the first appearance of Suoidea ( pigs) and the genus Hypertragulus calcaratus. In South America, it is located between the stages Mustersum and Tinguiriricum. ,

Final considerations

The Grande Coupure was undoubtedly a significant break in the faunal diversity, particularly in Europe. The linked with it extinction of species, mainly in mammals, but did not reach by far the dimensions of the "Big Five" (the " Big Five " ) designated events (Contact Ordovician / Silurian, Devonian / Carboniferous ( Kellwasser event), Perm / Triassic, Triassic / Jurassic and Cretaceous / Paleogene ).

In addition, the Grande Coupure ( lutetium ) to Lower Oligocene is at the Middle Eocene period not completely alone, but is accompanied by several smaller turning points.