The Triassic Period
251.9–201.4 million years ago · 51 million years long
The world recovers, and the first dinosaurs appear
The short version
The Triassic began just after the worst extinction in Earth's history, when almost everything had died. Land was one giant continent, Pangaea, with a hot dry interior. The first dinosaurs turned up late in the period and were small, fast and rare — nothing like the giants that came later.
The world then
All the continents were fused into Pangaea, stretching pole to pole, with a vast desert interior and monsoon belts along the coasts.
There were no ice caps, carbon dioxide was high, and the tropics were probably lethally hot for large animals for part of the Early Triassic.
Life in the Triassic
Recovery from the end-Permian extinction took several million years. Land was dominated first by therapsids and then by pseudosuchians — crocodile-line archosaurs — which stayed dominant for most of the period.
The oldest widely accepted dinosaurs, such as Herrerasaurus and Eoraptor from Argentina's Ischigualasto Formation, appear around 231 Ma and are metre-scale bipeds. Pterosaurs and the first true mammals also originate here.
Inside the Triassic
- Early TriassicPost-extinction recovery; no dinosaurs yet.251.9–247.2 Ma
- Middle TriassicArchosaurs diversify; dinosaur ancestors appear.247.2–237 Ma
- Late TriassicFirst true dinosaurs, small and uncommon.237–201.4 Ma
Best-documented Triassic dinosaurs
Genera whose entire known fossil range sits inside the Triassic, ranked by how many sites they turn up at.