The end-Triassic extinction opens the world to dinosaurs
A mass extinction wipes out the competition
Quick facts
- When
- About 201 million years ago, Triassic-Jurassic boundary
- Likely cause
- Massive volcanism tied to Pangaea's breakup (debated)
- What died out
- Phytosaurs, aetosaurs, and other competing land reptile groups
- Effect on dinosaurs
- Competitors removed; dinosaurs diversified afterward
What happened
At the end of the Triassic, about 201 million years ago, a mass extinction swept away many of the large land animals that had shared the world with the first dinosaurs, including groups like phytosaurs, aetosaurs, and other reptile relatives that had until then rivaled or outnumbered them. The U.S. National Park Service names massive volcanic eruptions, tied to the beginning of Pangaea's breakup, as the most likely primary cause, releasing gases that disrupted the climate and ocean chemistry. Both the National Park Service and the Natural History Museum are direct about the limits of that certainty: the Natural History Museum states the causes of this extinction are still hotly debated among scientists.
Why it matters
Dinosaurs had existed since about 240 million years ago without dominating their world; this extinction is the event that changed that. The Natural History Museum states plainly that once the competing large land animals were wiped out, dinosaurs survived and used the newly open niches to diversify and increase in number through the Jurassic and Cretaceous that followed. Without this clearing of the field, the rest of this timeline might look very different.
How we know
The U.S. National Park Service describes the extinction, its likely volcanic cause tied to Pangaea's breakup, and the land animal groups it eliminated. The Natural History Museum dates it to about 201 million years ago at the Triassic-Jurassic boundary, states outright that its causes remain disputed, and directly credits it with giving dinosaurs the opening to diversify.
Sources
- Natural History Museum, London. Where did dinosaurs come from? (Natural History Museum) (2024) · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- U.S. National Park Service. Extinction events (U.S. National Park Service) (2023) · Reputable sourcenps.gov · The domain "nps.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Natural History Museum, London. When did dinosaurs live? (Natural History Museum) (2024) · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Part of a timelineAge of Dinosaurs21 events · The age of the dinosaurs across the Mesozoic Era, from the Great Dying that cleared the way to the asteroid that ended their reign.View all →