Of all the creatures that once inhabited the earth, the most popular and the most exciting were the dinosaurs. These terrible lizards roamed the earth, around 230 million years ago, for over 165 million years. Although there are about 350 known species, fossils of new dinosaurs are still being discovered. There are two main groups of dinosaurs: the Sauropods that were largely herbivores, and the carnivorous Theropods.All dinosaurs were not monstrously huge. Some were as small as chicken. But about 65 million years ago, all the dinosaurs perished over a comparatively short period of time.What caused this puzzling extinction? There are two theories to explain this mass disappearance in which many other creatures also perished. About 60 to 70 per cent of all known species of plants and animals went extinct during the same period.According to one theory, a giant meteorite or comet crashed onto the earth at that time. This destroyed all life within the vicinity of the impact and created a huge cloud ofdust that spread over most of the earth. This cloud blocked out the sunlight, preventing photosysnthesis. As plants died, all the huge herbivorous dinosaurs dependent on the plants and the carnivores dependent on the herbivores, perished. The entire food chain was affected. Evidence to support this asteroid theory is the large concentration of iridium deposits found on earth during that time. Iridium is an element normally found in large amounts only in meteorites or comets and are normally present in only minute quantities on earth.Another theory holds massive volcanic eruptions responsible for the event. These eruptions were caused due to the drifting of continents and the consequent change in temperature. At some places the lava was as much as 2,400 m thick and may have extended to more than two million sqkm. Lava flows of such magnitude might probably have caused immense clouds of smoke which may have had the same series of effects on the food chain as the impact of an asteroid.And though thesemighty giants are no more on earth, the existing tell-tale signs speaks volumes of their life. Dinosaurs footprints have been vital source in understanding their behaviour - how fast they ran, whether they lived alone or in groups, how they cared for their young and how they sustained in the survival game as hunters or the hunted. While the bones enabled scientists to reconstruct the physical appearance of dinosaurs, reconstructing the life of the dinosaurs will always be a work of imagination. But their footprints are the closest we can come to the living reality of the dinosaurs world.According to scientists, dinosaurs were one of nature's experiments that failed. But if dinosaurs had survived the natural catastrophes, mammals would not have flourished and then man would have never been the dominant creature on earth. Dinosaurs "ruled" the world for about 165 million years. By comparison, Homosapiens - modern man - has been in existence for a mere 35,000 years. Dinosaurs may have become extinct in theend, but while they were alive, they were great survivors.
