Dinosaur is the name of a group of prehistoric reptiles that ruled 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 1800's. The name dinosaur comes from the term Dinosauria, which means terribly great 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 130 feet (40 meters) and weighed as much as 85 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.
The first dinosaurs appeared on 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, Diplodocus, and Tyrannosaurus. Apatosaurus (formerly called Brontosaurus) grew about 70 feet (21 meters) long. Diplodocus reached an even greater length
