At the Triassic-Jurassic boundary, the massive eruptions occurred in the fracture zone of the continental crust in the central part of Pangea.
The Triassic–Jurassic (Tr-J) extinction event, or the Triassic-Jurassic mass extinction (TJME), was a catastrophic event of the Mesozoic era and one of the six mass extinctions of the Phanerozoic eon. It marks the boundary between the Triassic and Jurassic periods, about 201.4 million years ago. The victims of this extinction became conodonts, placodonts, but, mostly, the various terrestrial vertebrates including parareptiles and all pseudosuchians except crocodylomorphs. Dinosaurs, pterosaurs and mammaliamorph cynodonts survived this event, and became widespread in the next Jurassic period. Many aspects of the Triassic-Jurassic extinction are poorly known and there are several theories to explain its causes, of which most scientists accept active volcanism.
Impact on fauna[]
Large ichthyosaurs like Ichthyotitan did not survive the Triassic-Jurassic extinction
The most visible sign of the disaster is the extinction of conodonts, a group of jawless animals that were abundant in the seas from the Cambrian to late Triassic. Only a small number of conodonts survived to the Early Jurassic, and they soon disappeared completely. Another obvious sign of TJME is a coral gap observed in the lower srtata of the Hettangian stage. But while these signs point to a global catastrophe, many aspects of TJME are still unknown due to a lack of fossils, especially of large animals, from both Rhaetian and Hettangian stages. For this reason, some researchers suggest that many groups of Triassic animals missing from the Jurassic deposits died out gradually, and not as a result of a cataclysm. In any case, several cephalopod groups as well as placodonts, nothosaurs and huge ichthyosaurs of the family Shastasauridae are not known from the strata younger than Raetian.
Orthoceratoids, a large group of cephalopods that asore in the Ordovician, were still numerous in Carnian and Norian ages, but none of them is known from Rhaetian and Jurassic strata. In 1994, Zhuravlevia, a cephalopod claimed to be an orthoceratoid, was found in the upper Aptian sediments of Caucasus, Russia, but was later reclassified as nautiloid.
It is believed that the continental fauna suffered the most from the extinction, altough the lack of fossils makes it difficult to estimate the number of extinct species. The main reason of this lack is the predominance of continental conditions on land in the Triassic, and so sedimentation processes were weak. Some animal groups like temnospondyls, dicynodonts and parareptiles were likely already small in number at the moment of the disaster. Very few temnospondyls are known from post-Triassic sediments. Hettangian and Sinemurian dicynodont tracks found in Lesotho were reported in the 1950s. Phytosaurs and such pseudosuchians as aetosaurs, rauisuchids and shuvosaurids were most likely still numerous in Rhaetian. All of them, with the possible exception of a few representatives, became extinct on the Triassic-Jurassic boundary.
Causes of the disaster[]
There are two main assumptions about the causes of extinction. Some researchers believe that 201 million years ago, a meteorite comparable to the one that caused the more famous Cretaceous-Paleogene extinction, fell on Earth. There are several impact craters that are associated with TJME. However, in most cases, the age of the craters does not coincide with the date of extinction, and their relatively small sizes raise doubts that such meteorites could have caused the global extinction.
Most researchers are inclined to believe that the extinction was not associated with the fall of cosmic bodies and was caused mainly by the gradual breakup of Pangea. Faults formed between diverging lithospheric plates, and magma broke through not to the seabed but to the surface of the continental crust, where it did not harden for a long time and had a strong impact on the environment. In the area of divergence of modern northern Africa, Europe, eastern North America and northeastern South America, рuge volumes of magma poured out, forming the largest plateau of volcanic origin. Today there are remnants of these erruptions known as the Central Atlantic Magmatic Province. Products ejected from the earth's mantle led to pollution of the atmosphere and oceans and to a volcanic winter. Large and ectothermic animals could not survive such events.
Aftermath[]
This extinction completed the transition phase between ancient and more advanced biota. With the disappearance of conodonts, new small species of animals spread into the seas. The development of plankton led to the emergence of giant filter feeders. On land, dinosaurs and pterosaurs entered a thriving phase. The extinction also gave impetus to the evolution of small cynodonts, among which true mammals eventually appeared.
In popular culture[]
- The Triassic-Jurassic extinction is briefly mentioned in the television series Walking with Dinosaurs very end of "New Blood", when "Time of the Titans" is announced.
- The extinction is covered in Episode 6 of Animal Armageddon (Strangled). Dinosaurs and pterosaurs like Staurikosaurus and Eudimorphodon, as well as the early mammaliamorph Megazostrodon, are depicted as survivors while archosaurs such as Desmatosuchus and Rutiodon went extinct.
- In the Netflix series Life On Our Planet, Pangaea is shown breaking apart, creating brand-new environments and causing the extinction of many. While the series' companion book acknowledges this event as the Triassic-Jurassic extinction, the show's narration does not.