Introduction
The Triassic extinction event occurred ~200 million years ago and formed the boundary between the Triassic and the Jurassic periods. During this event ~47% of genera were lost and ~80% of species (Barnosky et al. 2011). The number of events within this extinction event is disputed, with some studies suggesting that there were at least two periods towards the end of the Triassic period, ~12-17 million years apart. However, recent faunal analysis in the Petrified Forest of northeast Arizona suggests no significant change in the environment during this time (Hunt et al. 2002).
What was lost?
The Triassic extinction event was particularly severe in the oceans, with the conodonts disappearing, along with the majority of marine reptiles. Invertebrates such as brachiopods, molluscs, and gastropods were also severely affected (Raup and Sepkoski 1982).
(Triassic gastropod fossils. From: www.nationalgeographic.com)
The Triassic extinction event was not as equally devastating in terrestrial ecosystems, however a number of important clades of crurotarsans (large archosaurian reptiles) disappeared, as well as the majority of large labyrinthodont amphibians, groups of small reptiles, and a number of synapsids. Some primitive dinosaurs also went extinct, where other more adaptive dinosaurs survived to evolve into the Jurassic (Jacobs 1997).
Some of the surviving plants from the Triassic that went on to dominate the Mesozoic world include modern conifers and cycadeoids (McElwain and Punyasena 2007).
Postulated causes
The causes of the Triassic extinction event are not known with any certainty. The period was accompanied by huge volcanic eruptions that occurred as the supercontinent of Pangea began to break apart ~202-191 million years ago (Marzoli et al. 1999). This led to the formation of the Central Atlantic Magmatic Province (CAMP), which was believed to be one of the largest inland volcanic events since the planet stabilized (Barnosky et al. 2011).
Other possible causes for the extinction event includes global cooling or a bolide impact, however there is little evidence for these causes.
Conclusion
The Triassic extinction event left many empty niches, allowing the dinosaurs to expand and fill them. Over the next 150 million years dinosaurs became increasingly abundant, dominant, and diverse throughout the Jurassic and the Cretaceous, until the final event of the "big five" occurred, which will be discussed in the next entry.
References
Barnosky, A. D., et al. (2011). Has the Earth's sixth mass extinction already arrived? Nature. 471: 51-57.
Hunt, A. P., et al. (2002). No significant nonmarine Carnian-Norian (late Triassic) extinction event: Evidence from the Petrified Forest National Park. Denver Annual Meeting October 27-30. Paper no. 235-6.
Jacobs, L. L., (1997). African Dinosaurs. In Encyclopedia of Dinosaurs. Currie, P. J., K. Padian (Eds.). Academic Press. pp. 2-4.
Marzoli, A., et al. (1999). Extensive 200 million year old continental flood basalts of the Central Atlantic Magmatic Province. Science. 284: 618-620.
McElwain, J. C., and S. W. Punasna, (2007). Mass extinction events and the plant fossil record. Trends in ecology and evolution. 22: 548-557.
Raup, D. M. and J. J. Sepkoski, (1982). Mass extinctions in the marine fossil record. Science. 215. 1501-1503.
www.nationalgeographic.com
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