~230 million years ago (Late Triassic)Reputable sourceWell documented
The First Dinosaurs
On the timeline · around ~230 million years ago (Late Triassic) · The Triassic
What happened
The oldest definitive dinosaurs appear in ~230-million-year-old rocks of the Ischigualasto Formation in Argentina — small, bipedal forms such as Eoraptor and the early carnivore Herrerasaurus. They were still rare members of ecosystems dominated by other archosaurs.
Why it matters
These first dinosaurs were already recognisably dinosaurs, implying their lineage had been evolving even earlier. From this modest beginning came the dominant land animals of the next 165 million years.
Sources
- Natural History Museum. Where did dinosaurs come from? · Reputable source