Deep time
Dinosaurs lived a very long time ago, and for a very long time. Here’s how the Age of Reptiles is split up, and how it ended.
The Mesozoic Era, the age of the non-avian dinosaurs, lasted from about 252 to 66 million years ago. It’s split into the Triassic, Jurassic and Cretaceous periods. [source · checked 24 Oct 2026] Gideon Mantell came up with the phrase “Age of Reptiles”. [source]
About the dates: geologists keep refining period boundaries, so the figures below are exactly as given by the linked sources on 24 Oct 2026. If they’ve changed since, the source wins.
Triassic
The Triassic ran from 251.902 to 201.4 million years ago. It was the first and shortest period of the Mesozoic. [source · checked 24 Oct 2026]
- Dinosaurs first appeared in the Triassic, and became the dominant land animals after an extinction at the end of it. [source]
- Geologists keep refining these dates. The end of the Triassic has been pinned down more precisely in recent years, at 201.4 million years ago. [source · checked 24 Oct 2026]
Jurassic
The Jurassic ran from 201.4 to 143.1 million years ago. [source · checked 24 Oct 2026]
- The Jurassic is named after the Jura Mountains, on the border between France and Switzerland. [source]
Cretaceous
The Cretaceous ran from about 143.1 to 66 million years ago. It was the longest period of the Mesozoic. [source · checked 24 Oct 2026]
- Cretaceous comes from the Latin creta, meaning chalk. [source]
The end of the Cretaceous
- The extinction that ended the Cretaceous, around 66 million years ago, wiped out about three-quarters of the plant and animal species on Earth. [source · checked 24 Oct 2026]
- The rock layer from that moment is unusually rich in iridium, a metal more common in asteroids than in the Earth’s crust. [source]
- The asteroid idea was backed up by the discovery of the 180 km Chicxulub crater, under Mexico’s Yucatán Peninsula. [source]
- The Chicxulub crater was found by two geophysicists, Glen Penfield and Antonio Camargo, who were looking for oil. [source]
But not every dinosaur went. Birds are feathered dinosaurs. They evolved from theropods in the Late Jurassic, and they’re the only dinosaur lineage known to have survived the mass extinction about 66 million years ago. [source · checked 24 Oct 2026]