Triassic

In <a href="/facts/Paleontology/60n5yldd">paleontology</a>, the term Triassic denotes a <a href="/facts/Geologic_period/6LBR11yQ">geologic period</a> and a <a href="/facts/System_(stratigraphy)/eEt8kSgg">stratigraphic system</a> that spans 50.5 million years from the end of the <a href="/facts/Permian/CYgLgu5u">Permian</a> Period 251.902 Ma (million years ago) to the beginning of the <a href="/facts/Jurassic/o5Cy4KzX">Jurassic</a> Period 201.4 Ma. The Triassic Period is the first and shortest geologic period of the <a href="/facts/Mesozoic/yYsvXGPa">Mesozoic Era</a>, and the seventh period of the <a href="/facts/Phanerozoic/EKKuYnwl">Phanerozoic Eon</a>. The start and the end of the Triassic Period featured major <a href="/facts/Extinction_event/HloJubtR">extinction events</a>.
Chronologically, the Triassic Period is divided into three epochs: (i) the <a href="/facts/Early_Triassic/oBgudq2V">Early Triassic</a>, (ii) the <a href="/facts/Middle_Triassic/Y0FBoqA8">Middle Triassic</a>, and (iii) the <a href="/facts/Late_Triassic/TazKYWQN">Late Triassic</a>. The Triassic Period began after the <a href="/facts/Permian%25E2%2580%2593Triassic_extinction_event/d8kI8Mfn">Permian–Triassic extinction event</a> that much reduced the <a href="/facts/Biosphere/UpKAe1DB">biosphere</a> of planet Earth. The fossil record of the Triassic Period presents three categories of organisms: (i) animals that survived the Permian–Triassic extinction event, (ii) new animals that briefly flourished in the Triassic biosphere, and (iii) new animals that evolved and dominated the <a href="/facts/Mesozoic/yYsvXGPa">Mesozoic</a> Era. <a href="/facts/Reptiles/04n1uKf1">Reptiles</a>, especially <a href="/facts/Archosaur/Urd4MHfp">archosaurs</a>, were the chief terrestrial vertebrates during this time. A specialized group of archosaurs, called <a href="/facts/Dinosaur/JRdMqBnq">dinosaurs</a>, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period. Archosaurs that became dominant in this period were primarily <a href="/facts/Pseudosuchia/NBGrNAxx">pseudosuchians</a>, relatives and ancestors of modern <a href="/facts/Crocodilians/G4LbxJs6">crocodilians</a>, while some archosaurs specialized in flight, the first time among vertebrates, becoming the <a href="/facts/Pterosaurs/YNQwa1ru">pterosaurs</a>. <a href="/facts/Therapsids/P4ERDjA2">Therapsids</a>, the dominant vertebrates of the preceding Permian period, saw a brief surge in diversification in the Triassic, with <a href="/facts/Dicynodontia/dLcplJmI">dicynodonts</a> and <a href="/facts/Cynodontia/8Trvx14s">cynodonts</a> quickly becoming dominant, but they declined throughout the period with the majority becoming extinct by the end. However, the first stem-group <a href="/facts/Mammal/phSwTzBo">mammals</a> (<a href="/facts/Mammaliamorpha/D2eN8cH1">mammaliamorphs</a>), themselves a specialized subgroup of cynodonts, appeared during the Triassic and would survive the extinction event, allowing them to radiate during the Jurassic. <a href="/facts/Amphibian/r2BleD2W">Amphibians</a> were primarily represented by the <a href="/facts/Temnospondyli/lEoAzjJe">temnospondyls</a>, giant aquatic predators that had survived the end-Permian extinction and saw a new burst of diversification in the Triassic, before going extinct by the end; however, early crown-group <a href="/facts/Lissamphibia/zeV5XtE9">lissamphibians</a> (including stem-group <a href="/facts/Frog/IxYhbeda">frogs</a>, <a href="/facts/Salamander/5pKurkwV">salamanders</a> and <a href="/facts/Caecilian/Cpuye4Xn">caecilians</a>) also became more common during the Triassic and survived the extinction event. The earliest known <a href="/facts/Neopterygii/L8A9xsRq">neopterygian</a> fish, including early <a href="/facts/Holostei/aot3VGm4">holosteans</a> and <a href="/facts/Teleost/1YULPGW5">teleosts</a>, appeared near the beginning of the Triassic, and quickly diversified to become among the dominant groups of fish in both freshwater and marine habitats.
The vast <a href="/facts/Supercontinent/amID2KQp">supercontinent</a> of <a href="/facts/Pangaea/VGruHKJj">Pangaea</a> dominated the globe during the Triassic, but in the latest Triassic (<a href="/facts/Rhaetian/n7W4IUYz">Rhaetian</a>) and Early Jurassic it began to gradually rift into two separate landmasses: <a href="/facts/Laurasia/GechPqg3">Laurasia</a> to the north and <a href="/facts/Gondwana/zqbAvsnY">Gondwana</a> to the south. The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the <a href="/facts/Triassic%25E2%2580%2593Jurassic_extinction_event/5XKTUdt6">Triassic–Jurassic extinction event</a>, that wiped out many groups, including most pseudosuchians, and allowed dinosaurs to assume dominance in the Jurassic.

Triassic open-in-new

Triassic