When Were Dinosaurs Alive? Discover the Mesozoic Era

In this article, we ask ‘When were dinosaurs alive?’ and explore the different periods of the Mesozoic Era.

When Were Dinosaurs Alive?

Dinosaurs first appeared between 243 and 231 million years ago.

This was during the Triassic Period, which is part of the ‘geological timescale’. We’ll take a closer look at the geological timescale further down the page.

Dinosaurs lived on Earth for many millions of years. In fact, they were alive right up to the end of the Cretaceous Period, around 66 million years ago.

This means that dinosaurs were alive for as long as 177 million years, for much of the Triassic period, and for all of the Jurassic and Cretaceous periods.

A simple dinosaur timescale at the end of this article shows when dinosaurs were alive.

Geological Timescale

When Were Dinosaurs Alive Mesozoic Era Chart

You’ve probably heard of the Jurassic period – or at least the word ‘Jurassic’ – from the Jurassic Park films (which starred a T Rex, which was, er, from the Cretaceous period).

The Triassic, Jurassic and Cretaceous periods are all part of the geological timescale.

The geological timescale is used by geologists, paleontologists, and others who study long periods of time. Every period of the geological timescale corresponds to a particular layer of rock.

The Triassic period, for example, was the time during which the Triassic layer of rock was being formed.

Dinosaur fossil
The layer of rock in which fossils are found help us to know when dinosaurs were alive.

Newer layers of rock form on top of older layers. Therefore Jurassic rocks, formed in the Jurassic period, are found above rocks formed in the Triassic period.

This is very helpful when working out when dinosaurs were alive.

For example, dinosaur fossils found in rocks which we know were formed during the Triassic period are the same age as the rocks: making them between 252.17 and 201.3 million years old.

The geological timescale is overseen by the International Commission on Stratigraphy.

‘Eras’ are units of the geological timescale that are larger than periods. The Triassic, Jurassic and Cretaceous periods together make up the Mesozoic era.

When Were Dinosaurs Alive: A Simple Timescale

Spinosaurus Dinosaur
Spinosaurus was alive in the late Cretaceous period.

This simple timescale shows when dinosaurs were alive.

  • 252.17 million years ago: Triassic period begins
  • Between 243 and 231 million years ago: Dinosaurs appear, having evolved from primitive reptiles
  • Dinosaurs such as Eoraptor, Coelophysis and Plateosaurus are alive
  • 201.3 million years ago: A worldwide extinction event marks the end of the Triassic period.
  • 201.3 million years ago: Jurassic Period begins
  • Dinosaurs become the dominant land animals
  • Dinosaurs such as Allosaurus, Apatosaurus, Compsognathus and Stegosaurus are alive
  • Early birds such as Archaeopteryx appear
  • 145 million years ago: Cretaceous period begins
  • Dinosaurs such as T Rex, Ankylosaurus, Parasaurolophus and Velociraptor are alive
  • 66 million years ago: The Cretaceous–Paleogene Extinction Event causes the extinction of 75% of all species on Earth, including the dinosaurs.

When Were Dinosaurs Alive? Conclusion

Dinosaurs were alive throughout much of the Mesozoic era, which is divided into three periods: the Triassic, Jurassic and Cretaceous periods.

Dinosaurs appeared somewhere between 243 and 231 million years ago. They became extinct around 66 million year ago, when the Cretaceous–Paleogene Extinction Event caused the extinction of 75% of all species on Earth.

Dinosaurs were alive for between 177 and 165 years.

We hope that you have found this page useful. You can find lots more awesome dinosaur information throughout Active Wild. A good place to start would be one of these articles: