Editing Triassic (section)

==Triassic–Jurassic extinction event==
{{Main|Triassic–Jurassic extinction event}}
[[File:Extinction Intensity.svg|thumb|upright=1.2|The mass extinction event is marked by 'End Tr']]
The Triassic Period ended with a mass extinction, which was particularly severe in the oceans; the [[conodont]]s disappeared, as did all the marine reptiles except [[ichthyosaur]]s and [[plesiosaur]]s. Invertebrates like [[brachiopod]]s and [[mollusc]]s (such as [[gastropod]]s) were severely affected. In the oceans, 22% of marine families and possibly about half of marine genera went missing.

Though the end-Triassic extinction event was not equally devastating in all terrestrial ecosystems, several important clades of [[Crurotarsi|crurotarsans]] (large archosaurian reptiles previously grouped together as the [[Thecodontia|thecodont]]s) disappeared, as did most of the large labyrinthodont amphibians, groups of small reptiles, and most synapsids. Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived to evolve into the Jurassic. Surviving plants that went on to dominate the Mesozoic world included modern conifers and cycadeoids.

The cause of the Late Triassic extinction is uncertain. It was accompanied by huge [[volcano|volcanic]] eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago (40Ar/39Ar dates),<ref>Nomade et al., 2007 Palaeogeography, Palaeoclimatology, Palaeoecology 244, 326–44.</ref> forming the [[Central Atlantic Magmatic Province]] (CAMP),<ref>Marzoli et al., 1999, Science 284. Extensive 200-million-year-old continental flood basalts of the Central Atlantic Magmatic Province, pp. 618–620.</ref> one of the largest known inland volcanic events since the planet had first cooled and stabilized. Other possible but less likely causes for the extinction events include global cooling or even a [[bolide]] impact, for which an impact crater containing [[Manicouagan Reservoir]] in [[Quebec]], [[Canada]], has been singled out. However, the Manicouagan impact melt has been dated to 214±1 Mya. The date of the Triassic-Jurassic boundary has also been more accurately fixed recently, at {{Period start|Jurassic}} Mya. Both dates are gaining accuracy by using more accurate forms of radiometric dating, in particular the decay of uranium to lead in zircons formed at time of the impact. So, the evidence suggests the Manicouagan impact preceded the end of the Triassic by approximately 10±2 Ma. It could not therefore be the immediate cause of the observed mass extinction.<ref>Hodych & Dunning, 1992.</ref>
[[File:Petrified Forest National Park-Rainbow Forest Museum-1.jpg|thumb|Skull of a Triassic Period phytosaur found in the Petrified Forest National Park]]
The number of Late Triassic extinctions is disputed. Some studies suggest that there are at least two periods of extinction towards the end of the Triassic, separated by 12 to 17 million years. But arguing against this is a recent study of North American faunas. In the [[Petrified Forest National Park|Petrified Forest]] of northeast Arizona there is a unique sequence of late Carnian-early Norian terrestrial sediments. An analysis in 2002 found no significant change in the paleoenvironment.<ref>{{cite web |url=http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_42936.htm |title=No Significant Nonmarine Carnian-Norian (Late Triassic) Extinction Event: Evidence From Petrified Forest National Park |website=gsa.confex.com |access-date=2003-12-12 |archive-url=https://web.archive.org/web/20031106231251/http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_42936.htm |archive-date=2003-11-06}}</ref> [[Phytosaur]]s, the most common fossils there, experienced a change-over only at the genus level, and the number of species remained the same. Some [[aetosaur]]s, the next most common tetrapods, and early dinosaurs, passed through unchanged. However, both phytosaurs and aetosaurs were among the groups of archosaur reptiles completely wiped out by the end-Triassic extinction event.

It seems likely then that there was some sort of end-Carnian extinction, when several herbivorous archosauromorph groups died out, while the large herbivorous [[therapsid]]s—the [[Kannemeyeriidae|kannemeyeriid]] dicynodonts and the [[Traversodontidae|traversodont]] cynodonts—were much reduced in the northern half of Pangaea ([[Laurasia]]).

These extinctions within the Triassic and at its end allowed the dinosaurs to expand into many niches that had become unoccupied. Dinosaurs became increasingly dominant, abundant and diverse, and remained that way for the next 150 million years. The true "Age of Dinosaurs" is during the following Jurassic and Cretaceous periods, rather than the Triassic.