The first dinosaurs appear
Small, two-legged reptiles enter the fossil record in the Triassic
Quick facts
- First dinosaurs
- About 240 million years ago
- Period
- The Triassic, 252 to 201 million years ago
- What they were like
- Small and bipedal (two-legged)
- Status then
- Not yet dominant among reptiles
What happened
The Natural History Museum places the first dinosaurs in the fossil record around 240 million years ago, during the Triassic Period, which ran from 252 to 201 million years ago. These earliest dinosaurs were small, bipedal creatures, a modest start for a group that would go on to include the largest animals ever to walk the Earth. They shared the Triassic world with many other kinds of reptile and were not yet dominant.
Why it matters
This is the actual beginning of the dinosaurs, the group this whole timeline follows. They started small and unremarkable, and only after another extinction at the end of the Triassic did they rise to rule the land for the rest of the Mesozoic.
How we know
The Natural History Museum states that the first dinosaurs appear in the fossil record around 240 million years ago and describes them as small, bipedal creatures, within a Triassic Period it dates to 252 to 201 million years ago.
Sources
- Natural History Museum, London. The Triassic Period: the rise of the dinosaurs (Natural History Museum) (2024) · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Gnathovorax cabreirai: a new early dinosaur and the origin and initial radiation of predatory dinosaurs (PeerJ, 2019, via PubMed Central) (2019) · Peer-reviewed (author-declared)pmc.ncbi.nlm.nih.gov · Cited as a "journal" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- Natural History Museum, London. When did dinosaurs live? (Natural History Museum) (2024) · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Part of a timelineAge of Dinosaurs21 events · The age of the dinosaurs across the Mesozoic Era, from the Great Dying that cleared the way to the asteroid that ended their reign.View all →