Dinosaur fossil
Everything we know about dinosaurs comes from studying the fossils they left behind. Not every animal or plant that died in the distant past created a fossil. Usually, whatever was left of a dead animal was eaten by scavengers or gradually dissolved into the earth by the forces of air and water. Occasionally, however, the conditions were just right to transform certain parts of an animal’s body into a fossil that could be preserved for hundreds of millions of years.
The most frequent way for that to happen was if an animal’s body ended up in a place where it would be quickly covered with layers of sediment or sand, therefore protecting it from decay.
The most likely place for this to happen was on the sandy bottom of the sea or a lake or river. Many times, dinosaurs that died by rivers or lakes were washed away by the water to a sandbar or sank to the water’s bottom where their bodies were covered with soft sediment. It is also possible for dinosaurs to be fossilized in deserts where the fast-blowing sand could quickly cover up a body.
In either case, the soft parts of the dinosaur like the skin, muscles and organs eventually dissolved, leaving the harder parts like the skeleton and teeth preserved. Over the years, as more and more sediment covered the dinosaur’s remains, minerals replaced the material of the bones or teeth and left a hardened duplicate of the original bone.
Usually, the hardest parts of an animal were the only parts fossilized, but sometimes the soft tissue such as the skin or muscle could be preserved in its original state, and at times, trace fossils, such as footprints in soft soil, were preserved.