DINOSAUR [9 Sayfa]

Dinosaur is the name of a group of prehistoric reptiles that ruled the earth for about 160 million years. These animals died out millions of years ago, but they have fascinated people ever since they were first described in the early 1800s. The name dinosaur comes from the term Dinosauria, which means terrible lizards. But dinosaurs were not lizards, only distantly related to them, and most were not very terrible. Some of the best-known dinosaurs were terrifying, however. Many were of enormous size. Some dinosaurs towered above and weighed more than any other animal ever to live on land. The largest dinosaurs may have grown as long as 150 feet (45 meters) and weighed as much as 85 short tons (77 metric tons). Such giants would have been more than 10 times as heavy as a full-grown elephant. The only animals that grow to this size today are a few kinds of whales, and they live only in the water. Size was not the only characteristic that made some dinosaurs terrifying. Many large dinosaurs were fierce and deadly meat-eaters. DINOSAURSThe first dinosaurs appeared on the earth about 230 million years ago. They lived in nearly all natural settings, from open plains to forests to the edges of swamps, lakes, and oceans. Then about 65 million years ago, the dinosaurs died out. Dinosaurs varied greatly in how big they grew, how they looked, and where they lived. Some of the most famous were such gigantic animals as Apatosaurus «uh pat uh SAWR uhs», Diplodocus «duh PLAHD uh kuhs», and Tyrannosaurus «tih ran uh SAWR uhs». Apatosaurus (formerly called Brontosaurus) grew about 70 feet (21 meters) long. Diplodocus reached an even greater length—about 90 feet (27 meters). Both Apatosaurus and Diplodocus were plant-eaters. Each had a small head and an extremely long neck and tail. Tyrannosaurus was a fierce meat-eater. It stood almost 12 feet (3.7 meters) tall at the hips and had an enormous head and long, pointed teeth. But not all dinosaurs were giants. The smallest kinds were approximately the size of a chicken. In certain ways, dinosaurs were like many modern reptiles. For example, some dinosaurs had teeth and skin much like those of alligators living today. Many were probably about as intelligent as crocodiles and alligators. However, dinosaurs also differed from present-day reptiles in many ways. For example, no modern reptiles grow as large as the biggest dinosaurs. In addition, many kinds of dinosaurs were bipedal—that is, they walked on their hind legs. Dinosaurs also had a different kind of leg posture. Lizards, turtles, and most other modern reptiles hold their legs out to the sides of their body in a low, sprawling posture. But dinosaurs held their legs under their body, much like those of a bird, a horse, a dog, or a person. This upright posture enabled dinosaurs to walk on all four legs without dragging their bellies on the ground. Dinosaurs lived during most of the Mesozoic Era. This period in the earths history lasted from about 248 million to 65 million years ago. The Mesozoic is sometimes called the Age of Reptiles or Age of Dinosaurs because dinosaurs and other reptiles were the largest animals during that time. Dinosaurs belonged to a group of closely related animals called archosaurs «AHR kuh sawrs» (meaning ruling reptiles). However, not all archosaurs were dinosaurs. Other well-known members of this group included crocodilians (alligators and related animals) and pterosaurs «TEHR uh sawrs» (meaning winged reptiles). By about 65 million years ago, nearly all archosaurs and many other creatures had died out, and the Mesozoic Era came to an end. Scientists do not know why dinosaurs died out. For many years, scientists thought that dinosaurs had left no descendants (offspring). But since the 1960s, dinosaur research has indicated that birds descended from particular kinds of small, meat-eating dinosaurs. This research has led many scientists to classify birds as living dinosaurs. Scientists learn about dinosaurs by stud [Ödev Ýndir]