Triassic–Jurassic extinction

The Triassic–Jurassic (Tr-J) extinction event, often called the Triassic–Jurassic mass extinction (TJME) or end-Triassic extinction, marks the boundary between the Triassic and Jurassic periods, 201.4 million years ago. It represents one of five major extinction events during the Phanerozoic, profoundly affecting life on land and in the oceans.

In the seas, about 23–34% of marine genera disappeared; corals, bivalves, brachiopods, bryozoans, and radiolarians suffered severe losses of diversity and conodonts were completely wiped out, while marine vertebrates, gastropods, and benthic foraminifera were relatively unaffected. On land, all archosauromorph reptiles other than crocodylomorphs, dinosaurs, and pterosaurs became extinct. Crocodylomorphs, dinosaurs, pterosaurs, and mammals were left largely untouched, allowing them to become the dominant land animals for the next 135 million years. Plants were likewise significantly affected by the crisis, with floral communities undergoing radical ecological restructuring across the extinction event.

The cause of the TJME is generally considered to have been extensive volcanic eruptions in the Central Atlantic magmatic province (CAMP), a large igneous province whose emplacement released large amounts of carbon dioxide into the Earth's atmosphere, causing profound global warming and ocean acidification, and discharged immense quantities of toxic mercury into the environment. Older hypotheses have proposed that gradual changes in climate and sea levels may have been the cause, or perhaps one or more asteroid strikes.

Research history

The earliest research on the TJME was conducted in the mid-20th century, when events in earth history were widely assumed to have been gradual, a paradigm known as uniformitarianism, while comparatively rapid cataclysms as causes of extinction events were dismissed as catastrophism, which had been associated with biblical creationism. Consequently, most researchers believed gradual environmental changes were the best explanation of the extinction; prominent vertebrate palaeontologist Edwin H. Colbert suggested gradual changes in the seasonality of rainfall and eustatic sea level rise that decreased the available land area above sea level were the culprit.