252 – 201 million years ago

The Triassic

The Triassic period began in the aftermath of the Permian–Triassic extinction — the most severe mass extinction in Earth's history, which wiped out roughly 96% of marine species and 70% of terrestrial vertebrates.

Rise of the archosaurs

With ecosystems hollowed out, archosaurs — the lineage that would eventually give rise to crocodilians, pterosaurs, and dinosaurs — diversified rapidly. By the Late Triassic, small bipedal dinosaurs like Eoraptor and Herrerasaurus were stalking what is now South America.

Notable species

• • Coelophysis — a slender, hollow-boned predator known from fossil beds in New Mexico.
• • Plateosaurus — an early sauropodomorph, hinting at the giants to come.
• • Postosuchus — a crocodile-line apex predator, not a dinosaur but often mistaken for one.