Cretaceous Period
The last act of the dinosaurs — and the day everything changed.
The Cretaceous is the final and longest period of the Mesozoic Era, running from about 145 to 66 million years ago. It was the last great chapter of the dinosaurs, a warm world of shallow seas and the first flowering plants — and it ended in one of the most famous catastrophes in Earth's history.
GEOLOGIC POSITION
| Eon | Phanerozoic |
| Era | Mesozoic Era |
| Span | 145–66 Ma |
| Duration | ~79 million years |
| Preceded by | Jurassic |
| Followed by | Paleogene |
AT A GLANCE
| Climate | Warm 'greenhouse' world with high carbon dioxide and very high sea levels — little or no polar ice for much of the period. |
| Geography | The supercontinent Pangaea was breaking apart; the Atlantic widened, and a shallow Western Interior Seaway split North America in two. |
| Key life | The age of dinosaurs at its peak — Tyrannosaurus and Triceratops lived at its very end. Flowering plants spread for the first time, alongside marine reptiles and ammonites. |
The world then
Pangaea was splitting into the continents we'd recognize today. Sea levels were extraordinarily high, flooding continental interiors — a shallow sea even cut North America in half. The climate was warm and largely ice-free.
Life
Dinosaurs dominated the land, with icons like Tyrannosaurus rex and Triceratops appearing in the latest Cretaceous. The first flowering plants (angiosperms) diversified, while oceans teemed with ammonites and large marine reptiles.
How it ended
About 66 million years ago, a massive asteroid struck near Chicxulub in modern Mexico, triggering the Cretaceous–Paleogene (K–Pg) mass extinction. Roughly three-quarters of species, including all non-avian dinosaurs, vanished — clearing the way for the age of mammals.
Sources
Compiled by PaleoDex from open scientific data. Boundary ages follow the International Commission on Stratigraphy (ICS); descriptions draw on Wikipedia/Wikimedia. Where a fact isn't sourced, we leave it out rather than guess.
· Wikipedia · ICS International Chronostratigraphic Chart
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