Triassic Period

Triassic Period (₂₅₂–201 million years ago)

The Triassic Period marks the beginning of the Mesozoic Era and the origin of dinosaurs.

World & Climate

• Begins after the Permian–Triassic mass extinction, when ~90% of marine species and ~70% of land species died out.
• Continents are joined into the supercontinent Pangaea.
• Climate is generally hot and dry in the interior, with strong seasonal extremes.

Life & Ecosystems

• Early archosaurs (the group that includes dinosaurs, pterosaurs, and crocodile relatives) diversify.
• The first true dinosaurs appear in the Late Triassic (₂₃₀ Ma).
• Other major groups present:
  • Early mammal relatives (therapsids)
  • Large non‑dinosaur archosaur predators
  • Early pterosaurs (flying reptiles)

Early Dinosaurs

Early dinosaurs were generally:

• Small to medium‑sized
• Mostly bipedal (walking on two legs)
• Likely fast and agile

Examples of Late Triassic dinosaurs:

• Eoraptor – one of the earliest known dinosaurs, small and lightly built.
• Herrerasaurus – early predatory dinosaur.
• Plateosaurus – early large, long‑necked herbivore (a prosauropod).

The Triassic ends with another mass extinction event, which removes many competing reptile groups and sets the stage for dinosaurs to become dominant in the Jurassic.