About Dinosaur Eras
Non-avian dinosaurs lived during the Mesozoic Era, which lasted from about 252 million to 66 million years ago. The Mesozoic is divided into the Triassic, Jurassic, and Cretaceous periods. Dinosaurs did not all live at the same time.
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The Mesozoic Era
The Mesozoic lasted for more than 180 million years.
Learn MoreTriassic Period
The first dinosaurs appeared during the Late Triassic.
Learn MoreJurassic Period
Dinosaurs diversified dramatically during the Jurassic.
Learn MoreCretaceous Period
The Cretaceous saw many famous dinosaur groups reach their greatest diversity.
Learn MoreDinosaurs Were Separated by Huge Time Gaps
Stegosaurus and Tyrannosaurus were farther apart in time than T. rex and humans.
Learn MoreChanging Continents
Plate tectonics changed dinosaur evolution.
Learn MoreChanging Climate
The Mesozoic was generally warmer than today but not unchanging.
Learn MoreThe End of the Cretaceous
The Mesozoic ended 66 million years ago.
Learn MoreThe Mesozoic Era
The era began after the largest known mass extinction and ended with another global mass extinction. During that enormous span, continents shifted, climates changed, oceans opened, and dinosaur groups evolved and disappeared.
Triassic Period
Early dinosaurs were only part of a wider world of reptiles. The supercontinent Pangaea still joined most land together. By the end of the Triassic, dinosaurs were becoming more important in many ecosystems.
Jurassic Period
The Jurassic is famous for giant sauropods, stegosaurs, and predators such as Allosaurus. Pangaea continued to split apart, changing coastlines and climates. The earliest known birds and close bird relatives also appeared during this period.
Cretaceous Period
Tyrannosaurs, horned dinosaurs, duck-billed dinosaurs, ankylosaurs, dromaeosaurs, and many bird groups flourished. Flowering plants spread widely, and continents moved closer to their modern positions.
Dinosaurs Were Separated by Huge Time Gaps
Stegosaurus disappeared near the end of the Jurassic, roughly 80 million years before Tyrannosaurus rex lived. T. rex disappeared 66 million years ago. Popular culture often places dinosaurs together that never encountered one another.
Changing Continents
When continents split, populations became isolated and evolved independently. Sea level changes also divided land areas. These geographic changes help explain why different dinosaur groups are found on different continents.
Changing Climate
There were no permanent polar ice sheets for much of the era, yet rainfall, temperature, sea level, and atmospheric composition changed repeatedly. Fossil plants, soils, sediments, and isotope chemistry help reconstruct ancient climates.
The End of the Cretaceous
A large asteroid impact near today's Yucatán Peninsula was a major cause of the end-Cretaceous extinction. Massive volcanism and environmental stress also occurred around the same time. All non-avian dinosaur lineages disappeared, while birds survived.