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During which geologic periods did dinosaurs live?

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Illustration showing various dinosaur species drawn to scale and grouped by geologic era: Late Cretaceous, Early Cretaceous, Jurassic, and Triassic. Dinosaurs range from large species like Brachiosaurus and Tyrannosaurus to smaller ones like Velociraptor and Compsognathus, with a human silhouette included for size comparison. Measurement bars at the bottom indicate 1 meter and 3 feet for scale reference. — dinosaur A selection of dinosaurs grouped by the geologic interval in which they lived.

Dinosaurs lived during the Mesozoic Era, which spanned approximately 252.2 million to 66 million years ago. This era is divided into three geologic periods, all of which hosted dinosaur populations:12

Triassic Period: Dinosaurs first appeared during the Middle to Late Triassic, roughly 245 to 237 million years ago.13
Jurassic Period: Dinosaurs underwent a great radiation and became the dominant form of terrestrial animal life.415
Cretaceous Period: Dinosaurs continued to thrive as the dominant land animals until their extinction at the end of this period, approximately 66 million years ago.156

While most dinosaurs died out at the end of the Cretaceous, it is important to note that one lineage of dinosaurs evolved into birds during the Late Jurassic, meaning that dinosaurs as a group have persisted to the present day.15