Dinosaurs were around for roughly 165–180 million years, from about 245 million years ago until their mass extinction 66 million years ago.

How long were dinosaurs around?

  • Dinosaurs first appeared in the Middle Triassic, about 245 million years ago, as part of the Mesozoic Era.
  • They disappeared at the end of the Cretaceous, about 66 million years ago, in the Cretaceous–Paleogene (K–Pg) extinction.
  • That means dinosaurs were around for on the order of 165–180 million years, dominating land ecosystems for most of the Mesozoic Era.

Quick timeline snapshot

  • Triassic beginnings: First dinosaurs evolve and start to diversify.
  • Jurassic heyday: Dinosaurs become the dominant large land animals.
  • Cretaceous finale: Diversity peaks, then a giant asteroid impact helps wipe out all non‑bird dinosaurs about 66 million years ago.

If the entire history of Earth were a one‑day clock, dinosaurs would rule from a little after 10 p.m. until about 11:40 p.m.—and humans would show up only in the last seconds.

Fun perspective

  • A famous example: Stegosaurus (Late Jurassic, about 150 million years ago) went extinct around 66 million years before Tyrannosaurus rex ever lived in the Late Cretaceous.
  • So even inside that ~165+ million‑year dinosaur span, different species were separated by tens of millions of years—far longer than our entire species has existed.

TL;DR: When people ask “how long were dinosaurs around,” the best current scientific answer is: for roughly 165–180 million years, from about 245 to 66 million years ago.

Information gathered from public forums or data available on the internet and portrayed here.