End‑Triassic extinction event

Timing, scale and key losses

Stratigraphic and geochemical studies place the main pulse close to the formal T–J boundary. The event is recognized across global sections and is recorded in sedimentary successions and isotopic excursions. Losses included a whole class of marine organisms, the conodonts, which were primitive tooth‑bearing chordates. About one‑fifth of marine families were affected, and many reef builders and ammonoids suffered severe declines. On land, all large non‑dinosaurian crurotarsans (a group of archosaurs), several lineages of early mammals and near‑mammals such as therapsids, and many large amphibians including some temnospondyls were eliminated or greatly reduced.

Proposed causes and mechanisms

Researchers have proposed multiple, partly overlapping drivers. The most widely supported mechanism is extensive volcanic activity—most notably the eruptions that formed the Central Atlantic Magmatic Province—which released large volumes of greenhouse gases. Rapid injections of carbon dioxide and other gases likely warmed the climate, altered precipitation patterns, and caused ocean warming and deoxygenation. Geochemical signals such as carbon isotope shifts and mercury enrichments support a link to volcanism, though the precise pacing and magnitude remain under study.

• Climate warming: increased greenhouse gases driving temperature rise.
• Ocean change: acidification and anoxia that stressed marine life and reefs.
• Sea‑level and habitat shifts: altering coastal and shallow marine habitats.
• Other hypotheses: bolide impact(s) and gradual environmental deterioration have been suggested but are less strongly supported.

Ecological consequences and recoveries

The extinction removed many ecological incumbents and opened niches that were later filled by emerging groups. In particular, the decline of several dominant archosaur clades and other competitors is believed to have facilitated the diversification and eventual dominance of true dinosaurs (members of the wider archosaur radiation) in the Early Jurassic. Terrestrial floras also changed, with shifts in plant communities affecting herbivore resources and ecosystem structure.

Notable facts, uncertainties and significance

The End‑Triassic extinction is recorded globally and therefore is a fundamental marker in Earth history, falling within the Phanerozoic eon. Estimates of how rapidly the main pulses occurred vary: some data imply geologically rapid deterioration over short intervals, while other evidence indicates a more stepwise decline. At least half of the species known from certain fossil-bearing assemblages appear to have vanished, reshaping ecological niches worldwide. This crisis also occurred while the supercontinent Pangaea was beginning to rift, which may have influenced environmental responses. Ongoing work by scientists continues to refine the timing, causes and consequences of this complex extinction episode.

Further reading and resources

For introductions and technical summaries consult field guides and recent review articles that synthesize stratigraphy, paleontology and geochemistry across boundary sections. Additional resources map taxonomic losses and geographic patterns, and discuss how the event compares with other major Phanerozoic extinctions.

Key terms and sections referenced above: Triassic, Jurassic, extinctions, Upper Triassic, Phanerozoic, eon, oceans, species, class, conodonts, chordates, crurotarsans, dinosaurs, archosaurs, therapsids, temnospondyls, niches, Pangaea, scientists.