Copyright by Harcourt, Inc.

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2 Copyright by Harcourt, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Requests for permission to make copies of any part of the work should be addressed to School Permissions and Copyrights, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida Fax: HARCOURT and the Harcourt Logo are trademarks of Harcourt, Inc., registered in the United States of America and/or other jurisdictions. Printed in the United States of America ISBN Ordering Options ISBN (Grade 3 On-Level Collection) ISBN X (package of 5)

3 by Vita Jimenez illustrated by Lyle Miller Orlando Boston Dallas Chicago San Diego Visit The Learning Site!

4 When Did Dinosaurs Live? Dinosaurs lived millions of years ago. The time when the dinosaurs lived is called the Age of the Dinosaurs. The scientific name for this time period is the Mesozoic (MEH-suh- ZOH-ik) Era. There were no people on Earth during the time of the dinosaurs. People did not live until much, much later. 2

5 When the dinosaurs lived, Earth was a very different place than it is today. Scientists have slowly been able to figure out how Earth must have looked back then. For example, it might have been more peaceful. Scientists have been able to figure this out using signs that have been left behind on Earth. 3

6 There are many ideas about what Earth used to look like. Many scientists think that long, long ago one part of Earth was all land. The other part was all water. Dinosaurs lived all over the land. Over time, the land broke up into big parts. These parts became what we now call continents. The water parts became the different oceans, rivers, and other bodies of water that we know today. Pangaea Triassic World Jurassic World 4

7 Dinosaurs still lived on the land after it broke apart. When they died, they left bones behind. They also left other signs that they had lived there. Scientists have found dinosaur bones in almost every country on Earth. This means that there are very few places where dinosaurs did not roam. Laurasia Gondwanaland Cretacean World World of Today

8 What Do Fossils Tell Us? The remains or traces of dinosaurs are called fossils. Scientists study fossils to find out about life on Earth long ago. A fossil is often a part of an animal or plant that lived very long ago. For example, a fossil can be a horn, a tooth, or a bone. There is another kind of fossil. If an animal walks in the mud, it will leave footprints. Leaves may also make a print in the mud. As hundreds of years pass, these footprints and leaf prints turn to stone. 6

9 Fossils of dinosaur bones can help scientists understand a dinosaur s shape and size. Once they know the size of one bone, they can figure out the size of another bone. Soon, they can put a whole skeleton together. Scientists can also find out whether older life forms looked like plants and animals that live now. Scientists look carefully at today s world. They use what they see to help them understand how plants and animals lived millions of years ago. 7

10 To find fossils, scientists go to places where they think fossils might be. Sometimes fossils are found in the sides of mountains. Sometimes they are found in dry riverbeds. Fossils can be found anywhere. Scientists explore the ground and rocks in the area they select. If they find fossils there, they have an idea of where the original plant or animal lived. Next, they start digging. As soon as they find a fossil, they draw a map to show the location. 8

11 Finally, they carefully pick up the fossil. They dust off the dirt or loose rocks. They put the fossil in a safe place. Through studying fossils, scientists have learned that dinosaurs were reptiles. Scientists have also found out that there were more dinosaurs that ate meat than dinosaurs that ate plants. Those that ate plants had smaller jaws and many small, flat teeth. Plants are easy to chew! Those that ate meat had powerful jaws and sharp teeth. Chewing meat is more difficult. 9

12 How Much Do We Know About Dinosaurs? Dinosaurs came in many different sizes. Some were big and slow. Others were small and quick. Some plant eaters were small. Some were very big. Small dinosaurs like Protoceratops ate plants near the ground. Some very tall dinosaurs ate leaves from the tops of trees. One of the tallest plant eaters was Brachiosaurus (BRAK-ee-uh-SAW-rus). Brachiosaurus had long front legs and a very long neck. Some scientists think that these dinosaurs were taller than 42 feet. That s taller than six tall men standing on one another s shoulders. 10

13 A large meat eater was Tyrannosaurus rex (ty-ran-uh-saw-rus REX). This dinosaur had one of the biggest heads of all the dinosaurs. It had powerful jaws and sharp teeth. If T. rex s teeth broke off, it could grow new teeth! T. rex stood about 18 feet tall and weighed more than 6 tons. It must have been a truly frightening sight. The name scientists gave this dinosaur means all powerful king. 11

14 The smallest dinosaur was Compsognathus (KOMP-sog-NAY-thus). It was about the size of a chicken. It ate small lizards and insects. Scientists think that Compsognathus was a very fast runner. Its fossils show that it had long, strong legs. Scientists think it may have looked like a bird as it ran around on its hind legs. It may even have had feathers. It is possible that Compsognathus is a very early relative to some of the birds we know today. 12

15 How Did Dinosaurs Have Babies? Scientists think that all dinosaurs laid eggs, as reptiles do. These weren t the kind of eggs you d eat in an omelet for brunch. Some of these eggs were huge! Fossilized dinosaur eggs and nests were found in Montana in The fossils of these baby dinosaurs teeth showed that they were probably plant eaters. These fossil eggs came from a small dinosaur named Maiasaurus (MY-uh-SAW-rus). Its name means good mother lizard in Greek. 13

16 What Happened to the Dinosaurs? Dinosaurs have been extinct for millions of years. Scientists do not know exactly why they disappeared. Perhaps it was something none of them could escape. One idea is that dust of some kind blocked out the sun s rays. Without the sun s light, plants died. Without food, the plant eaters died. Then the meat eaters died, because they had nothing to eat either. Maybe the dust was caused by lava from erupting volcanoes. Or perhaps the dust was caused by a meteor hitting Earth. 14

17 Where Can We See Dinosaurs Today? Many people want to know about dinosaurs. Why are they so interesting? Is it because they were so different from animals that live today? Is it because they are extinct? You can learn more about dinosaurs by visiting dinosaur exhibits in museums. You can also read about dinosaurs in books or on the Internet. Maybe you ll grow up to be a scientist and make your own dinosaur discoveries. Who knows? Maybe you ll be the person who finds out what really happened during dinosaur times. 15

18 Glossary Brachiosaurus a plant-eating dinosaur that was more than 42 feet tall, with long front legs and a long neck Compsognathus the smallest dinosaur, which had strong legs and could run very fast continent one of the seven large land masses of the Earth extinct no longer living fossil the remains or traces of an animal or a plant that lived millions of years ago Protoceratops a small dinosaur that probably ate plants growing close to the ground Tyrannosaurus rex a large meat-eating dinosaur with a huge head, strong jaws, and sharp teeth 16

19 Think and Respond 1How is the text in this story divided? 2What word on page 9 is a synonym for soil or ground? 3How have we learned about dinosaurs? 4What did you learn from reading this story about what scientists do? 5How was the Brachiosaurus similar to the Tyrannosaurus rex? How was it different? 6What would you do if you found a dinosaur fossil in your backyard? Research Pick a dinosaur mentioned in this story and find out more about it. Share your findings with your class. School-Home Connection Plan a trip with your family to a natural history museum. Make sure you visit the area that tells about the dinosaurs.