1. Dinosaurs Were Special Land Animals

A dinosaur is not just any big old animal.

A dinosaur was a kind of reptile that lived on land. Reptiles are animals with scaly skin, like lizards and turtles today. But dinosaurs were special. Their legs went straight down under their bodies, like the legs of a dog or a horse. This let them stand tall and walk well. Other reptiles, like crocodiles, have legs that stick out to the side. Dinosaurs laid eggs, and they all lived on land, not in the sea or the sky.

• Dinosaurs were land reptiles with scaly skin.
• Their legs went straight down under their bodies.
• They laid eggs and lived on land.

2. Naming the Terrible Lizards

People found strange giant bones and did not know what they were.

Long ago, people dug up huge bones and teeth and felt puzzled. They had never seen an animal that big. About two hundred years ago, scientists in England studied these bones carefully. A scientist named Richard Owen looked at them and gave the animals a brand new name. He called them dinosaurs, which means terrible lizards. He did not mean bad. He meant amazing and powerful. Since then, people all over the world have found dinosaur bones and learned more and more.

• People found giant bones and felt puzzled.
• Richard Owen named them dinosaurs about 200 years ago.
• Dinosaur means terrible, or amazing, lizard.

3. How To Spot a Dinosaur

Use a few simple clues to check if an animal is a dinosaur.

How do scientists know if an old animal was a dinosaur? They look for clues, one at a time. First, did it live on land? Dinosaurs did not swim in the sea or fly in the sky. Second, did its legs go straight down under its body? That helped it stand tall. Third, did it live in the time of dinosaurs, millions of years ago? If the answer to all three is yes, then it was most likely a real dinosaur.

• Clue 1: it lived on land, not the sea or sky.
• Clue 2: its legs went straight down under it.
• Clue 3: it lived millions of years ago.

4. Three Dinosaurs To Meet

Let us meet a few real dinosaurs by name.

Here are three real dinosaurs. Triceratops had three horns on its face and a big bony frill. It ate plants and walked on four legs. Stegosaurus had tall pointy plates along its back and spikes on its tail. It also ate plants. Velociraptor was much smaller, about the size of a turkey. It walked on two legs and was quick on its feet. All three lived on land, had legs under their bodies, and lived in the time of dinosaurs.

• Triceratops had three horns and ate plants.
• Stegosaurus had plates on its back and ate plants.
• Velociraptor was small, fast, and walked on two legs.

5. You Be the Dinosaur Detective

Use your three clues to test some animals.

Now it is your turn to be a detective. Use your three clues: lived on land, legs straight down, and lived millions of years ago. Think about a pterosaur. It flew in the sky, so it was not a dinosaur, even though it lived back then. Think about a plesiosaur. It swam in the sea, so it was not a dinosaur either. Now think about Triceratops. It lived on land with legs under it. Yes! Triceratops passes all three clues.

• A pterosaur flew, so it was not a dinosaur.
• A plesiosaur swam, so it was not a dinosaur.
• Triceratops passes all three clues and is a dinosaur.

6. What We Learned

Three big ideas to take with you.

Let us remember the big ideas. A dinosaur was a land reptile with legs that went straight down under its body, and it laid eggs. People found their bones and named them dinosaurs, which means terrible, or amazing, lizards. To spot a dinosaur, we use three clues: it lived on land, its legs were under its body, and it lived millions of years ago. Now you know what made a dinosaur a dinosaur!

• A dinosaur was a land reptile with legs straight under its body.
• Dinosaur means terrible, or amazing, lizard.
• Three clues: land, legs under it, lived millions of years ago.

Mastery quiz

1. What kind of animal was a dinosaur?
   • A land reptile
   • A kind of fish
   • A flying insect
   • A furry pet
2. How were a dinosaur's legs different from a crocodile's?
   • They stuck out to the side
   • They went straight down under its body
   • It had no legs at all
   • Its legs were like fins
3. Which of these was a real dinosaur?
   • Triceratops
   • Pterosaur
   • Plesiosaur
   • Shark
4. Which clue helps show an animal was a dinosaur?
   • It swam in the deep sea
   • It flew in the sky
   • It lived on land millions of years ago
   • It lived in a house with people