A great example of a cast fossil is a natural mold of a dinosaur footprint that has filled with sediment and later hardened into rock. When a dinosaur walked over wet ground, it left an impression that can be preserved. Over time, sediments can fill in the imprint, and as the original material erodes away, it leaves behind a cast of the footprint.
Cast fossils form when minerals seep into the mold and create a replica of the original structure. This process highlights the importance of sedimentary environments in fossil formation, and it allows paleontologists to study the behavior and movement of ancient creatures. Cast fossils provide insight into the size and shape of the organism, making them invaluable to our understanding of prehistoric life.