Fossils are the petrified remains of living things. There are three types of fossil, and each type is useful in telling us how creatures lived millions of years ago.
The first type of fossil is part of the body of the creature, usually the hard part of the body like the shell or the skeleton, which is preserved as it was originally. The second type is a mould of the creature’s body, left in rock after the body itself has decayed, so that we can see exactly how the creature looked. The last type is the imprint of the animal’s footprint in the clay or mud which has hardened into rock over the years. All these types of fossil are very useful for telling us what sort of animals lived on the earth millions of years ago, animals which have long since died our or changed slowly as time passed to adapt themselves to different conditions.