Article by: Adam Manning
Edited by: Harry T. Jones and J. D. Dixon
The Triassic Period, from 251.902 +0.024 to 201.3 +0.2 million years ago, is the first period of the Mesozoic Era. It immediately followed The Great Dying that concluded the previous Permian Period, where approximately 70% of terrestrial vertebrate genera and 85% of marine species globally became extinct. All of the continents were fused into a supercontinent called Pangaea, roughly centred on the equator. Pangaea was surrounded by the Panthalassa Ocean and cut into by the Tethys Sea. The Triassic Period saw the recovery of life on Earth after the horrific extinction event, and the strange organisms that had the opportunity to evolve as a result.
Immediately following the End-Permian mass extinction, there was a rapid rise in temperature in the Early Triassic due to unusually high spikes of carbon dioxide in the atmosphere and chemical weathering, where the atmosphere caused rocks to break down. These harsh conditions forced the relatively larger terrestrial life away from the equator and suppressed the recovery of ecosystems. Thus, it took most of the early Triassic for plants and animals to diversify again. During this time, Lystrosaurus curvatus dominated terrestrial ecosystems, making up ~ 75% of the terrestrial fauna.
One of the fascinating occurrences after the End-Permian extinction event is the new and often bizarre life that appeared afterwards. This is due to adaptive radiation: when animals diversify into many new species over a relatively short time period filling a variety of empty niches. One example of this is the drepanosaurids, like Megalancosaurus, a group of arboreal lizards from the Middle Triassic with a strange combination of features associated with modern animals: a bird-like skull, chameleon-like feet and a prehensile tail, sometimes with a claw at the end.
However, the Triassic is most famous for being the period in which archosaurs diversified and thrived. The earliest known dinosaur, Nyasasaurus parringtoni, appeared in the Middle Triassic. At 2-3m long, this theropod lived in South Pangaea. Pterosaurs, another group of archosaurs, also evolved in this period, and included Eudimorphodon ranzii, from the Late Triassic. Reptiles also took over the seas. By the Middle Triassic, ichthyosaurs such as Contectopalatus atavus, from Germany, and Phalarodon, from China, were hunting in the great Panthalassan Ocean. Our own mammal ancestors evolved during this time period, such as Eozostrodon, Megazostrodon and Erythrotherium.
The Triassic ended in yet another mass extinction. The End-Triassic extinction is one of the big five mass extinctions in the history of life on Earth, and was most likely caused by the Central Atlantic Magmatic Province eruptions, where huge flood basalt eruptions caused major, rapid climate and sea-level change. It has been estimated that 46.8% of genera from the Triassic did not survive into the Jurassic, the next period in Earth’s history. Luckily for us, our mammalian ancestors were able to weather the storm, and just like at the start of the Triassic, this loss of life allowed other species to diversify and flourish. This gave rise to notably the most famous extinct animals of all time, the dinosaurs.
 The mid-Triassic of Tanzania, approximately 240 million years ago. An early dinosaur relative, Teleocrater, is feeding on a Cynognathus, with dicynodonts in the background. Artwork by Mark Witton. Available at: https://phys.org/news/2018-03-decade-fossil-perspective-triassic-period.html.
 Skeletal reconstruction of Megalancosaurus by Gregory S. Paul. Taken from Harris and Downs, 2002.
 An Erythrotherium parringtoni ventures out onto the forest floor, dwarfed by the trunks of the Heidiphyllum trees that surround it. Artwork by Jack Wood.
Information References and Further Sources
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 Chart drafted by K. M. Cohen, D. A. T. Harper, P. L. Gibbard, and J.-X. Fan (c) International Commission on Stratigraphy, August 2018. To cite: Cohen, K. M., Finney, S. C., Gibbard, P. L. & Fan, J.-X. (2013; updated). The ICS International Chronostratigraphic Chart. Episodes 36: 199-204. Accessed 28th January 2020.
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