THE DINOSAURS

Scientists believe that dinosaurs came into being about 180 million years ago and died out about 60 million years ago. Since dinosaurs were reptiles, they must have developed from reptiles that lived before them. The first reptiles appeared long before the dinosaurs. They were able to live in water and on land. They hatched eggs and the young ones had legs and lungs. They could breathe air and probably ate insects. The reptiles became larger and stronger. Some looked like big lizards and others like turtles. They had short tails, thick legs and big heads. They ate plants. The first dinosaurs to develop resembled their reptile ancestors. They were slender and probably no bigger than a turkey and, like a turkey, they walked on two legs. Some remained small, but others grew heavier and longer. There were even a few that were six metres long, weighing as much as an elephant. They had small heads and short, blunt teeth, which were only good for eating plants. They lived in low, swampy places. Then came the next period in the Age of the Reptiles. Some of the plant-eating dinosaurs became so large that even four legs could not support them on land. These were the largest of all the reptiles. The largest dinosaurs were probably the biggest animals that ever walked the earth. They had to spend most of their lives in rivers and swamps. One of these giants was the Brontosaurus, 25 metres long and weighing about 40,000 kilograms! At the same time, other dinosaurs were able to walk about on land. One of these, the Allosaurus, was 10 metres long, had sharp teeth and claws, and fed on the Brontosaurus and other plant eaters! Dinosaurs developed in many different ways, but none of them ever developed a good brain. One of the reasons dinosaurs disappeared may be that they were just not bright enough to know how to survive and escape from all their natural enemies. But some scientists believe that changes in the earth and in climate killed off the dinosaurs. Swamps dried up and mountains appeared, making life difficult for the dinosaurs that could not live on dry land. Also, changes in climate produced changes in vegetation, and since many dinosaurs were plant eaters, their food supply disappeared. Finally, as the earth began to have seasons, shifting from hot summers to snowy winters, dinosaurs could not adapt themselves to these changes and gradually became extinct. There are other scientists who believe that the dinosaurs disappeared because of an incident that happened 65 million years ago. An enormous asteroid hit the earth. There was a huge explosion and this caused tonnes of dust to be blasted into the earth's atmosphere. There was such a thick layer of dust covering our earth that it blocked out sunlight for as long as five years. That was how plants died and the dinosaurs were deprived of food. Eventually they starved to death.