Decoding Fossils of Dinosaurs

Dinosaurs lived on earth 65 million years ago. They lived on the earth much before any human being was born. They ruled the earth for over 165 million years, till 65 million years ago. They were huge monsters, even bigger than elephants. The word "dinosaur" was taken from a Greek word which means terrible lizard. But they weren't exactly lizards. Lizards are one type of reptile and dinosaurs are another type. Not all dinosaurs were giants. Some dinosaurs were no bigger than small dogs. The smallest kind was about the size of a chicken.
No human being has seen a living dinosaur but, scientists have many ways of learning about them. One important way is by studying fossils. Fossils give scientists a vast amount of information about ancient animal and plant life which have become extinct. They also helped them in finding out how long ago the animal or plant lived. As animals and plants die over the years they get covered up and buried into soil. The soft parts of their bodies rot away leaving behind only the hard parts like bones and teeth. These hard parts lose their original mineral composition or structure. Their remaining parts either get recrystallized or replaced by other minerals such as silica and iron pyrites. This is called a fossil. Recrystallization means exchange of one chemical by another within the skeleton which results in a coarser, perhaps heavier structure. Many fossils consist of original hard parts of the animal as well as minerals taken from the surrounding rocks. This process preserves the fossil's structure but increases its hardness and weight.
Plants don't have bones. Only animals have teeth and bones, what happens to plants? Bones and teeth are preserved without much change except that the organic matter in the cavities and tiny spaces in the bone decays, leaving behind the hard, mineral substance of the bone. The spaces left empty by decay get filled with minerals such as lime and silica. Teeth are usually preserved without much change as