YoU’Ve BeEn SeArChInG ThE OpEn PlAiNs Of SoUtHeRn MoNtAnA FoR ThReE DaYs Your team has been scanning the ground for hidden dinosaur remains Now you spot something promising at your feet It looks like a piece of bone You wave your team over and begin to dig You break up layers of rock with picks and jackhammers The sun beats down and your hands are caked with dirt For a long time there is nothing to see but dust and stones Then you see another bone This one looks larger than the first You dig more carefully now Bone by bone your team unearths the skeleton of a dinosaur Once the great body of the dinosaur is exposed you stand and admire your finding This skeleton is the remains of a great prehistoric creature You feel as though you are looking into the distant past 5
chapter 1 WhAt ArE DINOSAURS Dinosaurs are a group of reptiles that first walked Earth around 240 million years ago They lived during the Mesozoic Era which ended about 65 million years ago At this time an event occurred on Earth that killed many of the planet’s species including dinosaurs Scientists are still not certain what event caused this destruction The most popular theory is that an asteroid hit Earth and covered its surface with ash The resulting conditions killed plant life as well as many animals that depended on plants From then on dinosaurs were extinct DiG ThIs Over years of research scientists have learned that dinosaurs were a varied group The smallest species was the size of a chicken The largest was nearly as long as three school buses Today dinosaur fossils are found in rock all over the world Paleontologists determine the age of these fossils using radiometric dating This 6
method measures the radioactive elements in rock containing fossils This tells researchers how long ago a dinosaur lived However fossil study has taught paleontologists much more than when dinosaurs lived Fossils reveal what dinosaurs might have looked like and how they might have lived They also help us better understand the conditions of Earth millions of years before humans walked its surface Dinosaurs walked the planet for about 170 million years That’s 850 times longer than modern humans have existed 7
