Science
What were dinosaurs?
Quick answer
Dinosaurs were reptiles that lived on land from about 230 million years ago until most died out 66 million years ago. Birds are their living descendants.
In one sentence
Dinosaurs were a group of animals that ruled the land for over 160 million years, and their fossils show us what they were like.
Explained
The word dinosaur comes from Greek and means "terrible lizard". Dinosaurs lived in the Mesozoic Era, which is split into three periods: the Triassic, Jurassic and Cretaceous. The first dinosaurs appeared around 230 million years ago, and the last big ones died out about 66 million years ago.
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Dinosaurs came in every size. Brachiosaurus was a plant-eater taller than a house. Triceratops had three horns and a bony frill. Tyrannosaurus rex, a meat-eater, was up to about 12 metres long. Velociraptor was only about the size of a turkey, and it probably had feathers. Many dinosaurs laid eggs and some looked after their young.
Not every ancient reptile was a dinosaur. Flying pterosaurs and swimming reptiles, such as plesiosaurs, lived at the same time but belong to different groups.
How do we know all this? From fossils, the remains or traces of living things preserved in rock. Scientists called palaeontologists dig up bones, teeth, footprints and even fossilised eggs. See fossils. They use these clues to work out how dinosaurs looked and lived, but some details are still guesses.
What happened to them? Evidence shows that a huge asteroid hit Earth near what is now Mexico about 66 million years ago. It threw dust into the air, which cooled and darkened the planet for a long time, and many plants and animals died. The non-bird dinosaurs disappeared. But some small feathered dinosaurs survived and became birds, so there are still dinosaurs around today. Look at a sparrow and you are seeing one. Read about birds, reptiles and evolution.
Examples
| Dinosaur | Period | Diet |
|---|---|---|
| Stegosaurus | Jurassic | plants |
| Brachiosaurus | Jurassic | plants |
| Tyrannosaurus rex | Cretaceous | meat |
| Triceratops | Cretaceous | plants |
| Velociraptor | Cretaceous | meat |
Common mistakes
- "People lived with dinosaurs." Humans appeared tens of millions of years later.
- "All big prehistoric reptiles were dinosaurs." Pterosaurs and plesiosaurs were not.
- "Stegosaurus and T. rex met." Stegosaurus lived about 80 million years before T. rex, so T. rex is closer in time to us.
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Dinosaurs
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When did most dinosaurs die out?
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Related topics
Fossils
Fossils are the preserved remains or traces of plants and animals that lived long ago, usually found in sedimentary rock. They help scientists learn how life on Earth has changed.
Evolution
Evolution is the way living things change over many generations. Individuals with features that help them survive tend to have more young, so those features become more common over time.
Reptiles
Reptiles are cold-blooded animals with dry, scaly skin. Snakes, lizards, turtles, tortoises and crocodiles are reptiles, and most of them lay eggs on land.
Adaptation
An adaptation is a feature or behaviour that helps a living thing survive where it lives. A polar bear's thick fur and a cactus's spines are adaptations.
Amphibians
Amphibians are cold-blooded animals with thin, moist skin that live part of their lives in water and part on land. Frogs, toads, newts and salamanders are amphibians.
Birds
Birds are warm-blooded animals with feathers, wings and a beak. They lay hard-shelled eggs, and most can fly. Penguins, ostriches and parrots are all birds.