How Long Ago Did Dinosaurs Live?

How long ago did dinosaurs live? On this page you’ll find out when dinosaurs lived and how long they’ve been extinct.

We’ll also talk a little about the Triassic, Jurassic and Cretaceous periods, and the Mesozoic era: the ‘Age of the Dinosaurs’.

This page is part of our main Dinosaur Facts section.

How Long Ago Did Dinosaurs Live?

Megalosaurus was the first dinosaur to be named.

Dinosaurs first appeared between 243 and 231 million years ago.

They’re big numbers, so it’s worth writing them out in full so you can get an idea just how long ago it was ...

The first dinosaurs appeared between 243,000,000 and 231,000,000 years ago!

At this time, the world was going through what is known as the 'Triassic Period'. The Triassic period is part of the geological timescale. We'll learn more about this further down the page.

Dinosaurs died out around 66 million (66,000,000) years ago.

That means that dinosaurs lived for around 177 million (177,000,000) years.

We’ve only been around for around 2 million years, so we’ve still got a long way to go to beat the dinosaurs!

Are Dinosaurs Still Alive?

Helmeted Hornbill dinosaur
A modern day dinosaur: the Helmeted Hornbill

It’s not as crazy as it sounds! In fact, most scientists today consider birds to be dinosaurs! This is because modern classification systems (how living things are grouped) are concerned with how groups of animals ‘branch off’ to become new species.

Because a group of dinosaurs ‘branched off’ to become birds (over the course of millions of years), birds can be considered to be dinosaurs!

So, when we say that dinosaurs became extinct 66 million years ago, we’re actually talking about all of the dinosaurs that didn’t become birds – i.e. the ‘non-avian’ dinosaurs.

How Long Ago Did Dinosaurs Live: Geological Periods

How long ago did dinosaurs live? As a geologist!

You may have heard about periods of time such as the Triassic, Jurassic and Cretaceous periods, but do you know what these names actually mean?

They’re all geological periods, and part of the geological timescale. Geology is the study of rocks. Geological periods all relate to specific layers of rock.

The geological timescale is a way of looking at the history of the world that directly relates to the very stuff that the world is made of: rock!

For example, the Triassic period is the time during which rocks in the Triassic layer were formed.

The deeper the rock layer, the longer ago it was formed. Therefore, the Triassic period occurred before the Jurassic period, because the Triassic rock layer is deeper than the Jurassic rock layer.

The geological timescale has different divisions, just like hours are divided into minutes, and minutes are divided into seconds.

In the geological timescale, eras are divided into periods, which in turn are divided into epochs.

You can learn more about the geological timescale here: Dinosaur Periods.

Mesozoic Era (252.17 to 66 million years ago)

  • Triassic Period (252.17 to 201.3 million years ago)
    • Early Triassic Epoch (252.17 - 247.2 million years ago)
    • Middle Triassic Epoch (247.2 - 237 million years ago)
    • Late Triassic Epoch (237 - 201.3 million years ago)
  • Jurassic Period (201.3 – 145 million years ago)
    • Early Jurassic Epoch (201.3 to 174.1 million years ago)
    • Middle Jurassic Epoch (174.1 to 163.5 million years ago)
    • Late Jurassic Epoch (163.5 to 145 million years ago)
  • Cretaceous Period (145 – 66 million years ago)
    • Early Cretaceous Epoch (145 to 100.5 million years ago)
    • Late Cretaceous Epoch (100.5 to 66 million years ago)

How Long Ago Did Dinosaurs Live: The Triassic Period

Eoraptor resto. 01

The Eoraptor, shown above, was one of the earliest dinosaurs.

As we’ve seen, the earliest estimate as to when dinosaurs appeared was around 243 million (243,000,000) years ago.

Of course, dinosaurs didn’t just appear out of thin air. They evolved from primitive reptiles, which themselves had evolved from amphibians around 350 million years ago.

A group of early reptiles called Archosaurs became dominant in the early Triassic period. Prior to this, a group of animals called the Synapsids – which would go on to become mammals – had been in charge. Their time would come!

Archosaurs branched into crocodilians (which, with the greatest respect to modern-day crocodiles and alligators, haven’t really changed much over the years), pterosaurs (flying reptiles, such as Pterodactylus), and dinosaurs.

Dinosaurs appeared sometime during the middle or late epochs of the Triassic period.

The earliest dinosaur that we know about is the Eoraptor, a small predator that walked on two legs.

Of course, dinosaurs weren’t the only animals alive back then; insects, lizards, frogs, fish, turtles and other creatures had already made an appearance.

Triassic–Jurassic Extinction Event

Allosaurus was a Jurassic predator.

At the end of the Triassic period, around 201.3 million years ago, something caused over 50% of all species to become extinct. This is known as the Triassic–Jurassic extinction event.

We don’t know exactly what caused this; likely explanations include an asteroid impact, or volcanic activity.

Jurassic & Cretaceous Periods

Whatever it was that happened at the end of the Triassic period enabled the dinosaurs to become the dominant land animals in the Jurassic period.

During the Jurassic period, dinosaurs branched off into several types, including huge sauropods such as Diplodocus, and fearsome predators such as Allosaurus. The early birds, such as Archaeopteryx, also began to appear.

In the Cretaceous period, more of the familiar names appeared, including dinosaurs such as T Rex, Spinosaurus and Triceratops.

Cretaceous–Paleogene Extinction Event

Scientists believe that a large asteroid strike caused the extinction of the dinosaurs.

However, the age of the dinosaurs came to an end around 66 million years ago with the Cretaceous–Paleogene extinction event. This caused around 75% of all species to become extinct, including all of the dinosaurs that hadn’t evolved into birds.

You can read more about the Cretaceous–Paleogene extinction event here.

How long ago did dinosaurs live? Conclusion

Next time you’re asked ‘How long ago did dinosaurs live?’ here’s your reply:

Dinosaurs lived from somewhere between 243 and 231 million years ago right up to the Cretaceous–Paleogene extinction event, which occurred around 66 million years ago.

Dinosaurs lived for around 177 million years. That’s much longer than they’ve been extinct.

However, dinosaurs still exist – in the shape of birds – so strictly speaking they’re still alive!

We hope that you enjoyed this page. Feel free to link to it or to share it on social media using the buttons provided. You can find more awesome dinosaur information at our main Dinosaur Facts page.

You’ll find an illustrated list of dinosaurs here: Dinosaur List.