Eocene-Oligocene extinction event
Encyclopedia
The transition between the end of the Eocene
and the beginning of the Oligocene
, called the Grande Coupure in Europe
, occurring 33.9 ± 0.1 Ma, is marked by large-scale extinction and floral and faunal turnover (although minor in comparison to the largest mass extinctions
).
Most of the affected organisms were marine or aquatic in nature. They included the last of the ancient cetaceans, the Archaeoceti
.
This was a time of major climatic change
, especially cooling, not obviously linked with any single major impact or any major volcanic event. One cause of the extinction event is speculated to be volcanic activity. Another speculation is that the extinctions are related to several meteorite
impacts that occurred about this time. One such event happened near present-day Chesapeake Bay
, and another the Popigai crater
of central Siberia
, scattering debris perhaps as far as Europe. The leading scientific theory on climate cooling at this time is decrease in atmospheric carbon dioxide
, which slowly declined in the mid to late Eocene and possibly reached some threshold approximately 34 million years ago.
This boundary is closely linked with the Oligocene Oi-1 event, an oxygen isotope excursion that marks the beginning of ice sheet
coverage on Antarctica.
, and the arrival in Europe of Asian immigrants. The Grande Coupure is characterized by widespread extinctions and allopatric speciation
in small isolated relict population
s. It was given its name in 1910 by the Swiss
palaeontologist Hans Georg Stehlin
, 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 endemic European faunas before the break and mixed faunas with a strong Asian component afterwards. J. J. Hooker and his team summarized the break:
Whether this abrupt change was caused by climate change
associated with the earliest polar glaciations and a major fall in sea levels, or by competition with taxa dispersing from Asia, few argue for an isolated single cause. More spectacular causes are related to the impact of one or more large bolides in northern hemisphere at Popigai
, Toms Canyon
and Chesapeake Bay
. Improved correlation of northwest European successions to global events 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 of a mouse
-sized early Oligocene omomyid
, reflecting the better survival chances of small mammals, further undercut the Grand Coupure paradigm
.
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
and the beginning of the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, called the Grande Coupure in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, occurring 33.9 ± 0.1 Ma, is marked by large-scale extinction and floral and faunal turnover (although minor in comparison to the largest mass extinctions
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
).
Most of the affected organisms were marine or aquatic in nature. They included the last of the ancient cetaceans, the Archaeoceti
Archaeoceti
Archaeocetes, or "ancient whales", are a paraphyletic group of cetaceans that gave rise to the modern cetaceans.The archaeocetes were once thought to have evolved from the mesonychids, based on dental characteristics...
.
This was a time of major climatic change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
, especially cooling, not obviously linked with any single major impact or any major volcanic event. One cause of the extinction event is speculated to be volcanic activity. Another speculation is that the extinctions are related to several meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
impacts that occurred about this time. One such event happened near present-day Chesapeake Bay
Chesapeake Bay impact crater
The Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest known impact crater in the U.S...
, and another the Popigai crater
Popigai crater
The Popigai crater in Siberia, Russia is tied with Manicouagan Crater as the fourth largest verified impact crater on Earth. A large bolide impact created the diameter crater 35.7 ± 0.2 million years ago during the late Eocene . The crater is 1½ hours from the outpost of Khatanga...
of central Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, scattering debris perhaps as far as Europe. The leading scientific theory on climate cooling at this time is decrease in atmospheric carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, which slowly declined in the mid to late Eocene and possibly reached some threshold approximately 34 million years ago.
This boundary is closely linked with the Oligocene Oi-1 event, an oxygen isotope excursion that marks the beginning of ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
coverage on Antarctica.
Grande Coupure
The Grande Coupure, or "great break" in continuity, with a major European turnover in mammalian fauna about 33.5 Ma, marks the end of the last phase of Eocene assemblages, the PriabonianPriabonian
The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene epoch or series. It spans the time between and...
, and the arrival in Europe of Asian immigrants. The Grande Coupure is characterized by widespread extinctions and allopatric speciation
Allopatric speciation
Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
in small isolated relict population
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....
s. It was given its name in 1910 by the Swiss
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
palaeontologist Hans Georg Stehlin
Hans Georg Stehlin
Hans Georg Stehlin was a Swiss paleontologist and geologist.He specialized himself on vertebrate paleontology, particularly on the study of Cenozoic mammals. He published numerous papers on primates and ungulates...
, 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 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 PalaeotheriidaePalaeotheriidaePalaeotheres are an extinct group of herbivorous mammals related to tapirs and rhinoceros, and probably ancestral to horses. They ranged across Europe and Asia during the Eocene through Oligocene 55—28 Ma, existing for approximately ....
(distant horseHorseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
relatives), six families of artiodactyls (cloven-hoofed mammals) (AnoplotheriidaeAnoplotheriidaeAnoplotheriidae is an extinct family of even-toed ungulates , endemic to Europe during the Eocene and Oligocene 48.6—23.030 Ma, existing for approximately . They were, most likely, all terrestrial herbivores.-Taxonomy:...
, XiphodontidaeXiphodontidaeXiphodontidae is an extinct family of even-toed ungulates , endemic to Europe during the Eocene 40.4—33.9 Ma, existing for approximately .. They were, most likely, all terrestrial herbivores.-Taxonomy:...
, Choeropotamidae, Cebochoeridae, DichobunidaeDichobunidaeDichobunidae is an extinct family of early even-toed hoofed mammals known from the early Eocene to late Oligocene of North America, Europe, and Asia. Dichobunidae includes some of the earliest known artiodactyls, such as Diacodexis....
and Amphimerycidae), the rodent family Pseudosciuridae, the primate families Omomyidae and Adapidae, and the archontan family Nyctitheriidae.
- "Post-Grande Coupure faunas include the true rhinoceros (family Rhinocerotidae), three artiodactyl families (Entelodontidae, AnthracotheriidaeAnthracotheriidaeAnthracotheriidae is a family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, Elomeryx, first appeared during the Middle Eocene in Asia...
and Gelocidae) related respectively to pigSuidaeSuidae is the biological family to which pigs belong. In addition to numerous fossil species, up to sixteen extant species are currently recognized, classified into between four and eight genera...
s, hippoHippopotamusThe hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
s and ruminantRuminantA ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s, the rodentRodentRodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
families EomyidaeEomyidaeEomyidae is a family of extinct rodents from North America and Eurasia related to modern day pocket gophers and kangaroo rats. The family includes the earliest known gliding rodent, Eomys -References:...
, CricetidaeCricetidaeThe Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
(hamsterHamsterHamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s) and CastoridaeCastoridaeThe family Castoridae contains the two living species of beaver and their fossil relatives. This was once a highly diverse group of rodents, but is now restricted to a single genus, Castor.- Characteristics :...
(beaverBeaverThe beaver is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver and Eurasian Beaver . Beavers are known for building dams, canals, and lodges . They are the second-largest rodent in the world...
s), and the lipotyphlan family ErinaceidaeErinaceidaeErinaceidae is the only living family in the order Erinaceomorpha, which has recently been subsumed with Soricomorpha into the order Eulipotyphla...
(hedgehogHedgehogA hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand . There are no hedgehogs native to Australia, and no living species native to the Americas...
s). The speciose genus PalaeotheriumPalaeotheriumPalaeotherium is an extinct genus of primitive perissodactyl ungulate. George Cuvier originally described them as being a kind of tapir, and as such, Palaeotherium is popularly reconstructed as a tapir-like animal...
plus AnoplotheriumAnoplotheriumAnoplotherium is an extinct genus of ungulates which lived from the Late Eocene to the earliest Oligocene. It was first found in the gypsum quarries near Paris....
and the families Xiphodontidae and Amphimerycidae were observed to disappear completely.
- "Only the marsupialMarsupialMarsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
family Herpetotheriidae, the artiodactyl family Cainotheriidae, and the rodent families Theridomyidae and Gliridae (dormice) crossed the faunal divide undiminished."
Whether this abrupt change was caused by climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
associated with the earliest polar glaciations and a major fall in sea levels, or by competition with taxa dispersing from Asia, few argue for an isolated single cause. More spectacular causes are related to the impact of one or more large bolides in northern hemisphere at Popigai
Popigai crater
The Popigai crater in Siberia, Russia is tied with Manicouagan Crater as the fourth largest verified impact crater on Earth. A large bolide impact created the diameter crater 35.7 ± 0.2 million years ago during the late Eocene . The crater is 1½ hours from the outpost of Khatanga...
, Toms Canyon
Toms Canyon impact crater
The Toms Canyon impact crater is the site where one or more meteors struck the Atlantic continental shelf, about east of Atlantic City, New Jersey....
and Chesapeake Bay
Chesapeake Bay impact crater
The Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest known impact crater in the U.S...
. Improved correlation of northwest European successions to global events 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
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
of all European primates at the Coupure: the recent discovery of a mouse
Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
-sized early Oligocene omomyid
Omomyid
Omomyids are a diverse group of early primates that radiated during the Eocene epoch between about 55 and 34 million years ago . Fossils of omomyids are found in North America, Europe, Asia, and possibly Africa...
, reflecting the better survival chances of small mammals, further undercut the Grand Coupure paradigm
Paradigm
The word paradigm has been used in science to describe distinct concepts. It comes from Greek "παράδειγμα" , "pattern, example, sample" from the verb "παραδείκνυμι" , "exhibit, represent, expose" and that from "παρά" , "beside, beyond" + "δείκνυμι" , "to show, to point out".The original Greek...
.