Oligocene

The Oligocene is in Earth's history, a chronostratigraphic series (ie, a time interval) within the system of the Paleogene, formerly of the Tertiary. The beginning of the Oligocene is about 33.9 million years, the end is dated to before about 23.03 million years. The Oligocene was followed by the Miocene and it was preceded by the Eocene.

• 5.1 Europe 5.1.1 Early Oligocene
• 5.1.2 Late Oligocene

Naming and history

The name Oligocene (of Griech. Ὀλίγος = " little, small, weak" and καινός = " new, unusual " ) was proposed by Heinrich Ernst Beyrich 1857.

Definition and GSSP

The beginning of the Oligocene (and thus also the Rupelium - level ) is defined by the extinction of the foraminiferal genus Hantkenina. The upper limit (and therefore the lower limit of the Miocene and the Aquitaniums ) is well defined by several events. Characteristic is the basis of magnetic polarity chronozone C6Cn.2n, the first appearance of foraminiferal species Paragloborotalia kugleri and the extinction of calcareous nannoplankton - type Reticulofenestra bisecta (base of nannoplankton zone NN1 ). The GSSP ( = global calibration point ) for the base of the Oligocene ( and the base of Rupelium stage) is the Massignano profile in an abandoned quarry on the east side of the road from Ancona to Sirolo on the Adriatic coast near the village Massignano (Ancona, Italy ).

Subdivision

The Oligocene is divided into two stratigraphic levels:

• System: Paleogene ( 66 to 23.03 mya ) Series: Oligocene ( 33.9 to 23.03 mya ) Level: Chattian ( 28.1 to 23.03 mya )
• Level: Rupelium ( 33.9 to 28.1 mya )

Regional and previous publications even further stages names are used. They acquired a variety of reasons not international levels and will only be used regionally or have fallen into disuse because of inadequate definition.

Geography and climate

During the preceding Eocene Antarctica was still connected to Australia and South America, and formed a remnant of the southern continent Gondwana. This was the circumpolar ocean current that encircles Antarctica today, not yet available. Instead penetrated warm water on the coasts of the continents along until to the south. This makes the climate in Antarctica was much milder. This changed at the beginning of the Oligocene before about 33 to 34 million years, broke up as estuaries between Antarctica and the adjacent southern continents. For the first time could now form the circumpolar ocean current. The temperature dropped to about 5 ° C. worldwide In some parts of Antarctica, therefore, emerged for the first time since the Permian again large glaciers.

The growth of the glaciers led to a drop in sea level probably about 30 m. Numerous shelf seas silted up, making several new compounds developed country. Thus fell at the beginning of the Oligocene the Turgai Street, which had formed a shallow sea between Asia and Europe millions of years, dry. Even the once flooded Ebro Basin southwest of the Pyrenees was the mainland, resulting in the complete connection of the Iberian Peninsula with Europe. Tectonic shifts caused a split in the Tethys in the Mediterranean Sea in the west and the Paratethys in the east. The Paratethys was in the East of Europe today and was only temporarily with the Mediterranean and the Indian Ocean in conjunction. The Mediterranean was but opened to the Atlantic Ocean. The African continent still remained largely isolated from Europe and Asia. This should only change drastically in the Miocene.

Later in the Oligocene, the climate cooled even more and so it happened about 30 million years to extensive glaciations on Antarctica. The sea level dropped by from up to 150 m. The reason for this seems to be the complete separation of South America from Antarctica to have been, what a strong circumpolar enabled. Also, the sea between Norway and Greenland, which is likely to have had a similar effect on the northern hemisphere opened. The most consequential effect of the cooler and drier climate was in addition to the creation of additional land along the shelf edges, the spread of drylands. So in the Oligocene vast desert areas emerged.

In the Oligocene, the folding of the Alps and the uplift of the Rocky Mountains reached a climax.

Paleogeography in central Europe

In Germany at the time of the Oligocene ( about 30 million years ago ), the North Sea extended to the Lower Rhine and in the space of Kassel ( Hessen). East Germany was flooded up to the resin and to Leipzig ( Saxony) from the sea. Between the North Sea and the Tethys Sea in the rest of today's Alpine region strait spanned an approximately 300 km long and up to 40 kilometers wide. It ran from Kassel starting on the Wetterau Depression and the Upper Rhine Valley to Basel ( Switzerland ). At the north end of the Upper Rhine Graben was between Odenwald, Spessart, Taunus, Hunsrück and the Palatinate mountains an inland sea, that was almost ten times as large as the present-day Lake Constance. In this strait lived sharks, rays, and manatees. The most significant archaeological site of fossils from the Oligocene in Germany is the Doberg in frets.

Faunal

Europe

Early Oligocene

Due to the dry case, the Turgaistraße originated at the beginning of the Oligocene a land connection between Europe and Asia. This allowed many animal forms from the East to Europe to penetrate, what with climatic changes led to greater losses under the Europe's native fauna in the association. This faunal exchange at the beginning of the Oligocene was first described by the Swiss palaeontologist Hans Georg Stehlin in 1909 as the Grande Coupure. Among the victims of this Faunenaustauschs included most of the Palaeotherien. Only a few genera, such as Palaeotherium and Plagiolophus survived the Grande Coupure. The primates then disappeared almost entirely from Europe. Only the genus Pseudoloris survived somewhat longer in today's Spain, but died out in the Oligocene. Furthermore, the Leptictida that Apatemyiden and the last Ischromyiden with the genus Plesiarctomys succumbed. The extinction of tree or forest dwellers suggests that further spread more open habitats at the beginning of the Oligocene. In contrast, the marsupials in Europe survived without major losses.

Among the newcomers from Asia are particularly noticeable the first rhinos Europe. These were represented in the Oligocene of Europe by the hornless Hyracodonten and Amynodonten as well as the horned rhinos of Diceratheriinae and Menoceratherien. Among the Hyracodonten the sheep large Eggysodon immigrated at the beginning of the Oligocene to Europe. The Amynodonten were common from the beginning to the end of the era with Cadurcotherium in Europe. More Rhinos of the European Oligocene and were Ronzotherium Epiaceratherium. These animals later founded the successful tribe of Aceratheriinae. The western parts of Europe were also reached during the Oligocene by Paraceratherium, the largest land-living mammal of all time, which was widespread in Asia. In addition to the rhinos and his closer relatives emigrated at the beginning of the Oligocene with the Chalicotherien one another extremely successful group of odd-toed ungulates from Asia. The first genus reached the Europe was Schizotherium.

The cloven-hoofed animals were less affected by the large faunal exchange at the beginning of the Oligocene. Many European families and genera survived the transition into the Oligocene. Thus survived about the Dichobuniden with Dichobune, Tapirulus and Diplobune. The Cainotheriidae survived with the hare great shape Plesiomeryx and the larger Caenomeryx. However, even among the artiodactyls some lines, such as the Dacrytheriden, Xiphodontiden and Anoplotheriden died out. The reason for this may have been the superiority of gelociden ruminants which have forms like Gelocus, Lophiomeryx and Bachitherium reached a large abundance of forms in the Oligocene. Striking the Oligocene Artiodactyla were the big Anthracotherien that brought huge, hippo large forms with the genus Anthracotherium. Others, such as Bothriodon, Elomeryx and Methriotherium were small and similar in size to today's pigs. In the Oligocene and reached for the first time the giant pig -like Entelodonten with Entelodon Europe. Only the skull of these animals was up to 1 m long. In addition, the first close relatives of pigs appeared with the genera Palaeochoerus and Doliochoerus.

Even the robbers among mammals were subjected to a drastic change at the beginning of the European Oligocene. Relatively few were affected only the archaic Creodonten. Some forms, such as Pterodon died out, but as the representative of the genus Hyaenodon were replaced by Asian species. Far greater changes were subject to the members of the order Carnivora ( carnivores ). Thus came with Eusmilus on the first Nimravids, cat-like predators who trained huge saber teeth. Another genus of the family, Nimravus, had smaller teeth. She appeared slightly later, also in the early Oligocene. Another member of the Nimravids was Quercylurus, the largest predator of its era. He reached the size of a bear, and seems to have been a plantigrade. Among the Arctoiden Cynodictis disappeared at the transition to Oligocene, and was replaced by Aphicyonodon. Among the smaller predators of the Eocene were animals that resembled modern civets, as Stenoplescitis and the closely related genus Palaeoprinodon.

Among the small mammals falls in the early Oligocene, the first-time appearance of the Lagomorpha ( lagomorphs ) in Europe. Among the insectivores, the moles ( Eotalpa ) and shrews were dominant. The rodents were as already represented in the Eocene mainly by Theridomyiden and dormice ( Gliridae ). As new releases for the first time appeared on Modern Family as agitators, squirrels, beavers, and now restricted to North America Aplodontia. The croissants were represented approximately by Palaeosciurus, the beaver by Steno Fiber. In addition, for the first time appeared on the Eomyiden that were typical in the Oligocene and Miocene, but eventually became extinct. The most distinctive newcomer among small mammals, however, was Atavocricetodon, the first member of the Burrows ( Cricetidae ).

A oligozänes crocodile Europe was Hispanochampsa.

Late Oligocene

Further cooling of the Earth's climate has led to the spread of drylands, which probably sealed the doom of Palaeotherien with Plagiolophus, the most Anthracotheriden and the genus Entelodon in Europe. During the late Oligocene disappeared and the hyracodonten rhino and the rhinoceros Ronzotherium. In contrast, the Menoceratherien were dominant and out of früholigozänen genus Epiceratherium created the genera Menoceras and Protaceratherium. From this strain, the Menoceratherien developed until the early Miocene, the three groups of rhino Rhinocerotinen, Anthracerotherinen and Teleoceratherinen. The oldest known genus of Aceratherien, Mesaceratherium was still in the late Oligocene, as Brachydiceratherium, the first genus of Teleoceratherien. As previously Rhinocerotheride applies Menoceras. In addition, in the late Oligocene appeared the first to tapirs in Europe. These belonged to the genus Protapirus, apparently already a trunk, much like today's tapirs possessed.

Among the artiodactyls diversification of ruminants moschoiden was typical of the late Oligocene. These include the genera Prodremotherium and Bedenomeryx that had emerged from Gelocus. They had, in contrast to this longer legs and a modified canon leg.

Among the small animals the theridomyden rodents suffered heavy losses. Among the surviving genera included Blainvillimys and Issidoromys, a genre that developed hypsodont teeth. The dormouse and the Eomyiden brought forth several new genera. Significantly more different forms emerged, however, under the Cricetiden who appeared in numerous new genera with complex molars. One among them, Melissiodon, survived until the early Miocene and seems to have been arboreal.

In Europe, disappeared among the predators during the late Oligocene the major Nimravids how Eusmilus, Nimravus and Quercylurus. This, however, seems to have been a local operation. The Creodonten were in decline. The last disappeared in Europe with Hyaenodon at the end of the Oligocene. However, in Africa, they survived longer and came from there in the Miocene even briefly returned to Europe. In return, the carnivores ( Carnivora ) were spread further. Thus, the period from the genera Stenolescitis Palaeoprionodon and various other predators like Haplogale, Stenogale, and Proailurus. Proailurus was about the size of an ocelot and is considered the first genus of cats. In addition, the Amphicyoniden widespread. These were predators that might have looked like hybrid creatures, dogs and bears. The first forms of Oligocene were quite small unspecialized genera such Pseudocyonopsis and Cynelos, recalled their teeth to today's dogs. Another genus, Ysengrinia other hand, had a specialized carnivore teeth. Later Amphicyoniden reached the proportions of tigers and are likely to have similar hunted. However, they were probably slower but more persistent. Coinciding with the first Amphicyoniden dived with Cephalogale on the first bear. This genus seems to have evolved from the früholigozänen Amphicyonodon. With different genres popular in the late Oligocene and the mustelids.

Asia

The largest land animal in the Asian Oligocene and also the largest land mammal of all time was Paraceratherium, a giant hornless, with the rhinos related animal of up to 5 m shoulder height. Only the skull measured 1.3 m. The adult males are likely to have weighed about 15 tons. In addition, the Amynodonten were as hornless rhinoceros of the Oligocene typical of Asia.

North America

Cats like predators of the North American Oligocene were Hoplophoneus and Nimravus. Characteristic of the predator fauna of the Oligocene in North America were especially the dogs. Hesperocyon was a surviving genus from the Eocene and seems to have been in the early Oligocene the only Canide with stable fossil record. From this shape formed during the Oligocene, the three subfamilies of the dogs that Hesperocyoninae that Borophaginae and the still existing Caninae. The Hesperocyoninae are initially represented by Mesocyon, Enhydrocyon and Osbornodon, the first genus of Borophaginae is Otarocyon. The Caninae are known only by a lower jaw fragment, which likely come from an ancestor of the genus Leptocyon. Later in the Oligocene larger dogs from the tribe of Hesperocyoninen, some of which reached the size of small wolves emerged. These were Sunkahetanka, Philotrox, Enhydrocyon and Paraenhydrocyon. During the Oligocene Hesperocyoninae the dominant dogs constituted, the Borophaginae were still rather small in stature. They were represented by about Archaeocyon, Cynarctoides and Phlaocyon. The Caninae were represented by Leptocyon. In the late Oligocene, the canids reached in North America with 25 species never reached a diversity. Other mammals of the late Oligocene of North America were Protoceras, the oreodontide Leptauchenia, and the horse Miohippus actually.

Africa

The land connection between Africa and Eurasia was not fully developed in the Oligocene. So kept the continent until the Miocene a very peculiar mammalian fauna with distinctive elements. The dominant large herbivores of the Oligocene of Africa were the hyrax. They developed a large abundance of forms, including some very large forms. The cloven-hoofed animals occurred in the Oligocene of Africa still sparse. However, large forms such as the Anthracotherien already occurred. The mammoths were still significantly smaller and reminded remotely resembling today's elephants. The mammoths were still in Africa, limited their homeland. I also had the Embrithopoda another group of animals, which produced large herbivores. The best known representatives, the vast Arsinoitherium recalls, located on a rhino. However, it had two paired horns on the forehead and was not related to the rhinos, already living on other continents at the same time. Large carnivores were the Hyaenodontidae. However, they are relatively rare in the fossil record of the Oligocene of Africa. The primates were represented in the Oligocene of Africa by Apidium.