Triassic–Jurassic extinction event

The Triassic - Jurassic boundary in front of around 200 million years ago was accompanied by the fifth-largest mass extinction of Earth's history, which the conodonts and many other taxa were killed. There are several theories as to his statement, but the growing evidence in the direction of huge volcanic eruptions.

• 2.1 sea level and climate changes
• 2.2 Impact of an asteroid
• 2.3 Massive volcanic eruptions

Impact on the living world

Affected Faunengruppen

Most affected by the mass extinction at the Triassic - Jurassic boundary (English Triassic - Jurassic extinction event) was the class of meeresbewohnenden conodonts disappeared completely. Furthermore, a fifth of the time in the sea -based families were wiped out. The radiolarian the Entactinaria were reduced very drastically and the Spumellaria lost about two thirds of its taxa. The Albaillellaria were previously extinct in the Late Triassic.

On the mainland, all large Crurotarsi (not to the dinosaurs belonging archosaurs ) were destroyed with the exception of the crocodiles. It is off:

• The ( thecodonten ) subordinations of Proterosuchia (including the Proterochampsidae )
• Rauisuchia
• Phytosauria
• Aetosauria (including the Stagonolepididae ) and
• Ornithosuchia

• Erpetosuchidae
• Scleromochlidae and
• Trilophosauridae.

Also, many of the large amphibians such as the temnospondylen superfamilies

• Capitosauroidea
• Mastodonsauridae
• Metoposauroidea and
• Plagiosauroidea

As well as some Therapsida did not survive the Triassic - Jurassic transition. Also off the diapsiden Endennasauridae and the mammalian precursor of Traversodontidae. The overall balance of the mass extinction was devastating - it is thought that a little more than 50 percent of all former taxa were killed at this event.

New Releases Faunengruppen

Due to the decimation of the Archosauria many ecological niches were released that were taken mainly from the dinosaurs in the further course of the Jura and which then aufrückten to a dominant position on the mainland.

The following taxa made ​​after the Triassic - Jurassic boundary their initial appearance:

• Campylognathoididae ( Pterosauria )
• Gephyrosauridae ( diapside Lepidosauria )
• Heterodontosauridae and Scelidosauridae ( dinosaurs of the order Ornithischia )
• Megalosauridae ( dinosaurs of the suborder Theropoda )

Causes of mass extinction

As an explanation for the evolutionary turning point of the Triassic - Jurassic boundary following hypotheses are stated:

• Sea level changes and associated climatic changes.
• Impact of an asteroid
• Massive volcanic eruptions

Sea level and climate changes

Sea level and climate changes are relatively long temporal events. But the mass extinction at the Triassic - Jurassic boundary was a very sudden incision was made in about 10,000 to more than 50,000 years ago.

The sea level was at the Triassic - Jurassic boundary in a global eustatic depression (regression He1 ). Thereafter began the transgression of Hettangiums.

Impact of an asteroid

Time- quite close to the Triassic - Jurassic boundary are the Wells Creek crater, and the Red Wing crater in the United States and the crater of Rochechouart Chassenon in France. The Manicouagan impact structure in Canada is about 12 million years older.

Massive volcanic eruptions

In about the same time as the Triassic - Jurassic boundary, the massive basalt outpourings of the Central Atlantic Magmatic Province were carried out ( CAMP ) that released huge amounts of carbon dioxide, sulfur dioxide and aerosols in the atmosphere. The impact of this event on the global climate caused possibly a greenhouse effect, caused by the absorption of CO2 and SO2. The extent to which aerosols in turn could oppose their cooling effect is poor estimate.

Geochemical studies on intermediate soil profiles within the CAMP basalts in eastern North America found strong negative anomalies in the carbon isotope 13C (English negatitive carbon isotope excursion ) that indicate rapid climate change. This finding comes from the of found in the paleosols lignin and wax of leaves. Two enclosed Seesedimentprofile were examined. The thus -derived n- alkanes δ13C - curve shapes with their negative deflections were almost identical and could also be correlated with the largely marine profile of Saint Audrie 's Bay, Somerset ( England). It can be concluded that both the continental and the marine area had been affected simultaneously by the Triassic - Jurassic event. It was also found that the oldest basalts in Morocco at the same time leaked to the beginning of the mass extinction, whereas the oldest basalt flows in eastern North America are slightly more recent.

The Central Atlantic Magmatic Province (central Atlantic Magmenprovinz ) was one of the largest Magmenprovinzen the earth. Their eruptions are likely to raised levels of carbon dioxide in the atmosphere to a critical value and triggered simultaneously in the oceans a Biokalzifikationskrise ( obstruction of biological Kalkschalenbildung ). Perhaps it came additionally to a dissociation of Erdgashydraten ( such as Methanchlathrate ), as was already the case during previous mass extinction at the Permian-Triassic boundary.

Age

The Triassic - Jurassic boundary is been radiometrically dated to 199.6 million years BP. This age was determined by means of a Grenztufflage the top Rhätiums on Kunga Iceland (Queen Charlotte Islands ) in British Columbia. Whiteside and others also indicate an age of 201.4 million years for the border.