4 INTRODUCTION Dinosaurs roamed Earth for many millions of years The World of Dinosaurs Millions of years ago dinosaurs stomped dashed and glided around Earth Many grew to incredible sizes Others were very small Some hunted and ate meat Others grazed on plants All dinosaurs were reptiles Dinosaurs evolved and went extinct or died out during three time periods The first is the Triassic This period began 252 million years ago Back then Earth was much warmer than it is today The continents were one landmass It was
5 called Pangaea Pangaea The Jurassic Period was 201 million to 145 million years ago The Cretaceous came last The continents slowly separated during these time periods An asteroid hit Earth 66 million years ago This ended the Cretaceous Period Most dinosaurs went extinct But some survived They continued to evolve Birds are the living descendants of dinosaurs Sometimes dinosaur bones footprints eggs and other remains got preserved These are called fossils Scientists use fossils to learn more about dinosaurs Pterosaurs above and plesiosaurs below were not dinosaurs But they lived at the same time as dinosaurs
