A fossil is the prehistoric remains of a plant or animal. Fossils are typically preserved when they are buried under many layers of sand and mud. Under great pressure the sand and mud become sedimentary rock. Minerals seep into the fossil replacing the organic matter and creating a replica in stone.
A fossil can be a trace fossil or a body fossil. A body fossil is what was actual organic material from a creature or plant (like a bone). Trace fossils are signs of plant and animal activity that have been preserved in rock. For example, dinosaur tracks, trails and dung are all trace fossils.
Fossils exist all over the world. As hills erode, fossils become visible and a Paleontologist can find and remove them for study. Sometimes a small area only a few hundred feet across will be jammed with skeletal remains. This is called a "bone bed." A bone bed maybe the site of a sandbar on an ancient river. During floods, the bodies of many animals floated downsteam, grounded on the bar, and quickly got covered with silt and were preserved.
