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What are Dinosaurs?

Part of Dinosaur Week

There have been many different animals that lived in the place we now call home. Some prehistoric animals are closely related to the animals that live today, some not so much. One group of reptiles we like to talk about are the dinosaurs!

Some prehistoric animals get called dinosaurs but aren’t really dinosaurs at all! For example, pterosaurs are flying reptiles but do not belong to the Dinosaur classification. Same with the plesiosaur – it’s actually a marine reptile, not a dinosaur!

So When Is A Dinosaur A Dinosaur?

Animals have to meet specific requirements to be called a dinosaur:

  • Lived on land (not water, except some modern birds)
  • Laid eggs
  • Had legs perpendicular to their body (not just sticking out the sides)
  • Had two holes behind their eye sockets for strong jaw muscles to open wide and clamp down hard

They also lived specifically in the Mesozoic Era, which can be broken up into the Triassic, Jurassic, and Cretaceous Periods.

How do we know so much about dinosaurs? Fossils!


Fossils are the hardened remains of plants, animals, or other life that can be found in the ground. Fossils are formed when something dies and is covered in layers of mud and other compounds.

Over millions of years, water seeps into the animal's hard parts (like bones) and leaves behind minerals.

Those minerals replace the bone over time and create a rock in the shape of the animal that was once there! You can also find impressions which are things like footprints, leaf prints, or patterns from the skin, fins, or feathers left in the mud or rock. On the Isle of Skye, you can actually follow a trail of dinosaur footprints fossilised in the mud on the beach!

Watch this video from the Natural History Museum to learn more about how fossils are made.

How Fossils Are Made (Natural History Museum)

Fossils can help tell us a lot about how animals lived and what the environment was like at that time. For example, if they had sharp, cone-like teeth, they were carnivores; if they had flat, bumpy teeth, they were herbivores.

It’s important to know, though, that most living things did not become fossils, so while they are really good at telling us some things, we will never get a complete picture of what life was like just from fossils. That’s when we need to rely on things like geology (what the rocks and rock formations can tell us) and climatology (how the weather and climate develop).

Did You Know? Until last year, the only dinosaur bones found in Scotland had been found on the Isle of Skye? A palaeontologist from National Museums Scotland discovered a stegosaurus fossil on the island of Eigg, which means there were dinosaurs there during the Middle Jurassic Period – a period not many scientists know too much about!

Now try some of our activities, and send your photographs to us of how you get on.

Don't forget to send us your photographs and enter our competitions to win some prizes.

Enter Competition

Free eBook About Dinosaurs (PDF)
Free eBook About Dinosaurs (PDF) from Free Kids Books
Dinosaurs At Natural History Museum
Dinosaurs (Natural History Museum)
Make A Model Dinosaur Activity
Dinosaur Game (BrainPOP)
Dinosaur Songs: T-Rex, Velociraptor & More (StoryBots)
Eigg Beach Runner Stumbles On Dinosaur Bone (BBC News)
Eigg Beach Runner Stumbles On Dinosaur Bone (BBC News)

This page is part of the Dinosaur Week information.

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