Grande Coupure

In paleontology , the Grande Coupure is an important exchange of fauna that took place at the turn of the Eocene / Oligocene ( Priabonian / Rupelian border ) about 33.9 million years ago. This incision was associated with a major extinction of species and a marked drop in temperature both on land and in the oceans. A large part of the Palaeotherien (early horses ), primates (master animals) , Creodonta (primal carnivores) and other animal groups fell victim to the greatly changed environmental conditions. New forms then replaced the extinct taxa.

History and terminology

The term Grande Coupure , French for 'large (one) cut', was coined in 1909 by the Swiss paleontologist Hans Georg Stehlin and introduced into scientific literature. In English , the term Eocene-Oligocene extinction event or sometimes just MP 21 event is used (MP for Mammal Paleogens ).

Effects

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

• About 60% of the Eocene mammal genera died out at the beginning of the Rupelian (Lower Oligocene).
• 66% of the mammal genera that existed during the Rupelian did not exist in the Eocene (so in the Rupelian 13 completely new families with 20 new genera appear).

Overall, the Grande Coupure led to an evolutionary upheaval, diversification and fauna renewal (fauna exchange).

The following groups of fauna were affected by extinction at the turn of the Priabonium / Rupelium :

Affected groups of fauna

The primitive insect eater Leptictidium auderiense

• Apatotheria ( shrew-like ), their family
  • Apatemyidae died out completely.
• Artiodactyla ( Artiodactyla ). Were less affected but lost some lines among the:
  • Anoplotherioidea
  • Dacrytheroidea
  • Xiphodontoidea
  • The Choeropotamidae family died out.
• Carnivora ( predators ) were badly affected.
  • Their superfamily Arctoidea ( marten-like , seals , bears etc.) lost the genus Cynodictis , which was replaced by Amphicyonodon .
• Cetacea ( whale ). The Basilosauridae , a side branch of the Archaeoceti , probably died out immediately after the Grande Coupure .
• Creodonta (primal carnivores). They were relatively unaffected. Pterodon became extinct, Hyaenodon was gradually displaced by Asian taxa.
• Insectivora ( insect eater ). They lost the Amphilemuridae and the Nyctitheriidae .
• Leptictida (early insectivores). They died out completely.
• Mesonychia . They also went out completely.
• Perissodactyla ( odd-toed ungulate )
  • Equidae ( horses ). The Palaeotheriidae (an ancient horse branch) were badly hit with them. Only a few genera survived, such as Palaeotherium and Plagiolophus , which also died out 2 million years after the faunal cut.
  • Tapiroidea ( tapirs ). They lost the families:
    • Isectolophidae
    • Lophialetidae
    • Lophiodontidae
• Primates ( master animals ). They disappeared almost completely from Europe with the extinction of the Plesiadapiformes , only the taxon Pseudoloris survived in Spain , but then also died out during the Oligocene.
• Proboscidea ( trunk animals ). They lost the early form of barytherium .
• Rodentia ( rodents ). With them the families ended:
  • Isochromyidae (squirrel relatives)
  • Protoptychidae
  • Reithroparomyidae
  • Sciuravidae

Newly published groups of fauna

Eusmilus , a Nimravide who appeared after the Grande Coupure

New publications in the rupelium were:

• Artiodactyla with the
  • Gelocidae
  • Hyptragulidae
  • Leptomerycidae
• Carnivora with the
  • Felidae (cats) Eusmilus , Nimravus and Quercylurus
• Chiroptera ( bats ). The following families emerged immediately after the Grande Coupure
  • Megadermatidae
  • Phyllostomatidae
• Insectivora with the
  • Soricidae ( Soricoidea )
• Lagomorpha ( hare-like )
• Perissodactyla ( odd-toed ungulate ) with the
  • Chalicotheriidae ( Ancylopoda )
  • Tapiridae
• Rhinocerotoidea , including the
  • Amynodontidae with Cadurcotherium
  • Hyracodontidae with Paraceratherium
  • Rhinocerotidae with Epiaceratherium and Ronzotherium
• Rodentia ( rodents ), including the
  • Aplodontia
  • Castoroidea (beaver) with stenofiber
  • Caviomorpha . All families (restricted to South America) are likely to have emerged from an original form that emerged on the Grande Coupure .
  • Cylinderodontidae
  • Eutypomyidae
  • Heteromyidae
  • Myomorpha with Eomyidae
  • Sciuroidea (squirrel) with Palaeosciurus
  • Tsaganomyidae

According to JJ Hooker et al. (2004), the Grande Coupure in Europe is characterized by the transition from a purely endemic fauna to a mixed fauna with Asian elements. For them, the fauna before was Grande Coupure distinct from perissodaktylen family of palaeotheriidae , 6 artiodaktylen families ( Amphimerycidae , anoplotheriidae , Cebochoeridae , Choeropotamidae , Dichobunidae and Xiphodontidae ) of the rodent family Pseudosciuridae by the two primate families omomyidae and Adapidae well as the very primitive insectivore family of Nyctitheriidae .

The fauna of the Eocene-Oligocene extinction event includes real rhinoceros (family Rhinocerotidae ), three artiodaktyle families (Anthracotheriidae, entelodont and Gelocidae, precursor respectively. Hippos, pigs and ruminants), the rodent families Castoridae (Beaver), Cricetidae (hamster) and insectivores family Eomyidae (Hedgehog).

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

Geochemical trends in deep sea sediments

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

• Most noticeable is a very rapid increase in the δ ¹⁸ O values , the so-called oxygen anomaly Oi 1 . This indicates a pronounced temperature drop in the world's oceans at the Eocene-Oligocene border. A general drop in temperature had already begun at the end of the Ypresium , but the drop in temperature during the Grande Coupure was striking at 1 ‰ δ ¹⁸ O PDB. Only in the Chattium did the temperatures stabilize again.
• From the Grande Coupure onwards , a very clear increase in the strontium isotope ratio of ⁸⁷ Sr / ⁸⁶ Sr begins , which continues into the Neogene . Increased strontium isotope ratios indicate increased sediment input, which is triggered by increased orogenic activities.
• Coupled with the increase in the oxygen isotope ratio, a slight short-term increase in the carbon isotope δ ¹³ C can be observed (also by just under 1 ‰), which decreases again in the course of the rupelium and then falls back below the old level in the chattium . This somewhat peculiar finding (normally the carbon values ​​fall with increasing oxygen values) can possibly be explained by an increased biological production in the world's oceans.
• (At least) two iridium anomalies have been discovered in sediments of the Priabonian period , which are associated with meteorite impacts and possibly accelerated the general cooling trend.

Possible causes

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

• plate tectonics
• climatic changes
• Meteorite impacts

Plate tectonic causes

• Continued northern drift of the southern continents away from Antarctica .
• Opening of the North Atlantic between Greenland and Norway .
• Alpine orogenetic movements (unfolding and elevation of the Alps , Pyrenees , Rocky Mountains etc.).

Climatic changes

The climatic changes were causally linked to the plate tectonics or to the continental drift based on it. Due to the north drift of the southern continents of Australia and South America, new inlets emerged, namely the Tasmanian Passage and the Drake Passage , which meant that the land mass of Antarctica was geographically and thermally isolated from now on, the latter due to the creation of the strongest ocean current on earth, the Antarctic Circumpolar Current . In the northern hemisphere, the North Atlantic opened up and thus enabled a connection to the polar sea.

These new constellations caused the sea temperatures to cool down to a depth of 5 ° C. At the same time, the first glaciations occurred on Antarctica . As a result, as a feedback effect, sea ​​levels fell by around 30 meters and shelf seas fell dry, including the Turgai Strait between Europe and Asia . This enabled Asian groups of fauna to penetrate Europe and initiate the faunistic upheavals of the Grande Coupure .

The global drop in temperatures had a serious impact on flora and fauna. For example, if subtropical vegetation still existed in Europe during the Eocene, extensive steppe areas were able to establish themselves from the Grande Coupure due to the cooler and at the same time drier climate. The endemic fauna of Europe was therefore exposed to multiple evolutionary stresses caused by new food competitors, global cooling and the associated environmental changes.

In the late Eocene, around 35 million years ago, the atmospheric CO ₂ concentration was still in the range of 1000 ppm. Parallel to the global cooling that occurred 33.7 million years ago, the growth of the Antarctic ice sheet marked the beginning of the Cenozoic Ice Age . Within a very short period of time, the CO ₂ concentration decreased by 40 percent and possibly sank even lower for several millennia. The causes of this rapid climate change according to geological standards are still unclear in some details.

Extraterrestrial causes

As with other large faunal cuts in the fossil record, extraterrestrial causes are also brought up for the Grande Coupure . For example, the meteorite craters of Chesapeake Bay and Toms Canyon can be classified very close in time (they are about 1 million years older) on the Grande Coupure . In contrast, the age of the 90 to 100 km diameter Popigai crater in northern Siberia is 33.7 million years according to a new date. This impact event is therefore directly on the Eocene-Oligocene boundary and could be causally linked to the mass extinction of that time.

Age

The turning point Priabonium / Rupelium and with it the Grande Coupure is absolutely dated with 33.9 ± 0.1 million years BP . The GSSP for this event is located in marine layers near Massignano in Italy . It is defined by the disappearance of the planktonic hantkeninid foraminifera (last appearance of Turborotalia azulensis ). The GSSP also corresponds to the end of the planktonic foraminifera stage P 17 within the nannofossil zone NP 21 and lies within the magnetic anomaly C 13r.1.

The first Asian faunas can be found in northwestern Europe in the Lowest Oligocene around 33.5 million years, i. H. the Grande Coupure extended over a period of about 350,000 years.

Dating using land mammal fauna communities

A detailed chronology was drawn up for the paleogene based on the found associations of land mammals (English land mammal ages or LMA ). These fossil fauna communities are very different for the individual continents, consequently each continent has its own chronological levels (Asia = ALMA , Europe = ELMA , North America = NALMA and South America = SALMA ).

In Europe is the Grande Coupure between stages Headonium and Suevium or between the stages MP 20 and MP 21, characterized by the last occurrence (engl. Load appearance date or LAD ) of the Xiphodontidae and shortly thereafter the Amphimerycidae well as Palaeotherium ; first occurred (Engl. first appearance or FAD ) the Castoridae , Cricetidae , entelodon and Rhinocerotidae .

In Asia, is Grande Coupure as Mongolian circulation (Engl. Mongolian Revolution ) means that between stages Ergilium and Shandgolium done. In North America, which is Grande Coupure between stages Chadronium and Orellum , characterized 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 Mustersum and Tinguiriricum levels .

Final consideration

The Grande Coupure (last “peak” on the right) compared to other mass extinctions during the Phanerozoic

The Grande Coupure was undoubtedly a significant turning point in fauna diversity (see mass extinction ), especially in Europe. The species extinction associated with it , mainly in mammals, did not reach the extent of the events known as the “Big Five” (Wenden Ordovician / Silurian , Upper Devonian ( Kellwasser event ), Permian / Triassic) , Triassic / Jurassic and Cretaceous / Palaeogene ).

In addition, the Grande Coupure in the Middle Eocene ( Lutetian ) to Lower Oligocene period is not a singular event, but is flanked by several smaller turning points.

See also

• Oligocene

literature

• F. Gradstein, J. Ogg, A. Smith: A Geological Time Scale . Cambridge University Press, 2004, ISBN 0-521-78673-8 .

Web links

• Original work by Stehlin from 1909

Individual evidence

1. ↑ Stehlin, HG: Remarques sur les faunules de Mammifères des couches eocenes et oligocenes du Bassin de Paris . In: Bulletin de la Société Géologique de France . 9, fourth series, 1909, p. 488-520 .
2. ↑ ^{a b} Hooker, JJ, Collinson, ME & Sille, NP: Eocene-Oligocene mammalian faunal turnover in the Hampshire Basin, UK: calibration to the global time scale and the major cooling event . In: Journal of the Geological Society . tape 161 , 2004.
3. ↑ Coccioni, R. et al .: Marine biotic signal across a late Eocene impact layer at Massignano, Italy . In: Terra Nova . tape 12 , 2000, pp. 258-263 .
4. ↑ Mark Pagani, Matthew Huber, Zhonghui Liu, Steven M. Bohaty, Jorijntje Henderiks, Willem Sijp, Srinath Krishnan, Robert M. DeConton: The Role of Carbon Dioxide During the Onset of Antarctic Glaciation . (PDF) In: Science . 334, No. 6060, December 2011, pp. 1261-1264. doi : 10.1126 / science.1203909 .
5. ↑ Becky Oskin: Russia's Popigai Meteor Crash Linked to Mass Extinction . livescience, June 13, 2014.
6. ^ I. Premoli-Silva & DG Jenkins: Decision on the Eocene-Oligocene boundary stratotype . In: Episodes . tape 16 , 1993, pp. 379-382 .