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What happened during the end-Triassic mass extinction?

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Triassic paleogeography — Triassic Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the early Triassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The end-Triassic mass extinction, occurring approximately 201 million years ago, was a global event that resulted in the loss of roughly 76 percent of all marine and terrestrial species.1

Biological Impact

In the marine environment, the event caused the extinction of conodonts and many ceratitid ammonoids, as well as numerous families of brachiopods, gastropods, bivalves, and marine reptiles. On land, a significant portion of the vertebrate fauna disappeared; however, groups such as dinosaurs, pterosaurs, crocodiles, turtles, mammals, and fishes were relatively unaffected. Many researchers believe this turnover opened ecological niches that allowed dinosaurs to become the dominant land animals. Notably, plant diversity remained stable across the Triassic-Jurassic boundary.12

Potential Causes

The cause remains a subject of debate, though many scientists point to intense volcanic activity associated with the rifting of the supercontinent Pangea. This volcanism likely released massive amounts of carbon dioxide, strengthening the greenhouse effect, raising global temperatures, and acidifying the oceans. Other theories suggest the release of methane from permafrost, extraterrestrial impacts, or sea-level changes as contributing factors.12