It is probably safe to say that some of the largest animals that have ever lived on the surface of this planet are members of a group of animals which has been collectively called dinosaurs. These ‘terrible reptiles’ as their name means, have excited the imagination of men ever since bones of the first dinosaurs were discovered in the rocks of Upper Triassic ago. Many tales have been told of these monsters sharing the Earth with man, but, of course, as we shall explain all the dinosaurs had died out long before man appeared.
Dinosaurs evolved into a great variety of different shapes and sizes but they all have a common ancestor. They ranged in size from dinosaurs the size of a chicken, to others which where as much as 30 meters long and weighing more than 30 tonnes. Some dinosaurs, such as the Diplodocus, lived on plants. Others where hunters. They attacked and killed dinosaurs as much as 15 meters long for food. Tyrannosaurus, better known as T-Rex, was the largest meat-eating animals that have ever dwelled on land. Bones of these animals have been discovered in rocks dating back to 70 million years in North America. There were also dinosaurs that lived in the sea. Others such as Pteranodon developed a kind of wing and they could glide in the upward currents of air that occur above the cliffs on which they must have lived.
Some of the less terrible dinosaurs could escape the predatory ones using their speed, but others were much clumsy and slow-moving to get away. They developed armoured coverings to their bodies to protect them and had spines and horny plates as well. In fact, Stegosaurus was probably able to defend itself quite well with the help of spikes at the end of its long tail.
Dinosaurs have presented researchers with many puzzles, not least of which is how giants like Brontosaurus managed to live at all. Examination of its bones has shown that its legs were probably not strong enough to support its weight on land, and if it lived partly submerged in water, its rib cage may have collapsed. On the other hand, it did not possess the correct kind of feet to survive in swamps.
There have been many arguments about why the dinosaurs suddenly died out. Perhaps the climate changed. In the 1980s, scientists found evidence of a disaster about 65 millions ago. It may have been caused by impact of a huge meteorite, which threw up dense clouds of dust around the Earth.
