The first dinosaurs
Small, fast, bipedal animals appear in Argentina — and are, for now, thoroughly unremarkable.
- When
- Known to
- ± 2 million years
- Era
- Triassic, Mesozoic
The oldest unequivocal dinosaurs, about 231 million years old, come from the Ischigualasto Formation of Argentina: Eoraptor, Herrerasaurus and Eodromaeus, none longer than a few metres. For the first thirty million years of their existence dinosaurs are a minor component of ecosystems dominated by crocodile-line archosaurs and therapsids. Their later dominance is not foreshadowed by anything about their beginnings.