What are Dinosaurs?

Ancient books and tales, tell of unusual, reptile-like creatures that once roamed the earth. There seem to have been many different types of such gigantic reptiles, both large and small. Early cultures, from Europe to China, gave many different names to them. The people of long past in Europe called them 'dragons'. Many of their descriptions of dragons sound similar to the description of the creatures that we today call dinosaurs.

Dinosaurs have captured the imagination of man, since the discovery of their fossils, due to their size and due to their mysterious disappearance. The term 'dinosaur' was coined by Sir Richard Owen (a Victorian anatomist) in 1841. It derives from two Greek words which mean 'terrible or fearsome lizard'.

Dinosaurs are said to have roamed the earth over 230 million years ago. Going from fossils found, scientists theorise that there may have been a wide range of dinosaurs with over 500 genera. Dinosaurs are classified under Archosaurs, which is Greek for ruling lizards. Within the group, dinosaurs are further classified by their gait. Though both crocodiles and dinosaurs fall under the same category, dinosaurs have their legs extended directly beneath the body while crocodiles have their legs sprawled on either side.

Types of Dinosaurs

Dinosaurs varied both in eating habits and size. They can be broadly classified into carnivores such as the Tyrannosaurus Rex and herbivores such as the Diplodocus. Dinosaurs also varied by size. On the taller side were the Sauropods and on the shorter were the Theropods such as the Microraptor, which was less than 2 feet in height. One of the tallest dinosaurs is considered to be the Argentinosaurus, which was estimated to be 85 feet in length. Dinosaurs not only came in all shapes and sizes but temperaments as well, from the towering and terrifying Tyrannosaurs to the docile and rhino-like Triceratops.

Dinosaurs evolved different defence mechanisms. The Stegosaurus, for example, was notable for its armoured plate-like protrusions on its back. Other dinosaurs such as the Triceratops had massive horns that they used to defend themselves against predators.

As these massive beasts lumbered across the prehistoric land, there were giant dinosaurs flying in the air above. These dinosaurs had wingspans up to 12 metre. One such dinosaur was the Pterosaurs, which resembled a blend between a giant bird and bat. These mighty beasts were able to walk on all fours when they did not take to the skies. In the seas, huge marine reptiles were the dominant species. In fact, the Ichthyosaurs, which were fish reptiles, are said to have appeared much earlier than the dinosaurs.

What are Dinosaur Fossils?

Dinosaur fossils are the bones of dinosaurs that are preserved in stone. The first fossils were discovered in 1819 in England. Dinosaur fossils are found in the earth's sedimentary layer. Moving river water deposits a layer of sedimentary rock. Animal fossils that are found in this layer were trapped by running water and were buried and preserved. Fossils are important as they help us to draw inferences about not only the types of dinosaurs but also information about how they lived their lives. It also helps in identifying the time period in which a certain dinosaur lived and therefore chart how the dinosaur may have evolved over time. Fossils range in sizes. They can be microscopic to huge in terms of the size of dinosaur bones.

Theories on Death of the Dinosaurs

Some scientists theorise that the so-called dragons of old could have been remnants of the ancient dinosaurs. Another group of scientists maintains that modern day birds are evolved forms of dinosaurs. However, most scientists theorise that the dinosaurs went extinct approximately 65 million years ago. They put forward two main theories on why dinosaurs died. The first states that extinction was a result of extensive weather changes at the end of the Cretaceous period. These changes affected the ecosystem and caused a drastic decrease in plant life. Consequently, herbivorous animals first started to die out, followed by the death of carnivorous animals.

One theory states that the extinction event was an impact event—an asteroid hit the earth. The dust cloud that resulted due to this event blocked sunlight, which in turn, caused the plant life to die out. Another variation of this theory states that instead of one huge asteroid hitting the earth, a number of smaller asteroids hit the earth simultaneously.

The other theory that has been put forth regarding the death of dinosaurs is that they gradually died out due to a change in climate. This change was caused due to global cooling and a fall in the sea level. Cold-blooded creatures were not able to adapt to this change. Added to this, there was a lot of volcanic activity at the end of the Cretaceous period.

The problem with most extinction theories is that they cannot explain why certain animals die out and why certain survived. Even so man will always remain enchanted with these mighty beasts that once roamed the earth.