It is probably sate to say that some of the largest animals that have ever lived on the surface of this planet are members of group of animals which have been collectively called dinosaurs. These ‘terrible reptiles’, as their name means, have excited the imagination of men ever since bones of the first dinosaur were discovered in rocks of Upper Triassic age that is deposits about 200 million years old. Many tales have been told of these monsters sharing the Earth with man, but of course, all the dinosaurs had died long before man appeared.
Dinosaurs evolved into a great variety of different shapes and sizes but they all had a common ancestor. They ranged in size from dinosaur the size of a chicken, to other which were as much as 30 meters long and weighing more than 30 tonnes. Some dinosaurs, such as Diplodocus, lived on plants. Others were hunters. They attacked and killed dinosaurs as much as 15 meters long for food. Tyrannosaurus were the largest meat eating animals that have ever dwelled on land. Bones of these animals have been discovered in rocks about 70 million years old in North America. There were also dinosaurs that lived in the sea. Others such as pteranodon develop a kind of wing and they could glide in the upward current 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 too clumsy and slow moving to get away. They developed armored covering 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, scientist found evidence of a disaster about 65 million year ago. It may have been caused by the impact a huge meteorite, which threw up dense clouds of dust around the Earth.