Question

This is a fossil made when an organism buried in sediment decomposes, leaving a hollow area showing part or all of the organism's structure.
GPT-4o mini
The fossil you are describing is known as a **cast fossil** or **mold fossil**. Specifically, a mold fossil is created when an organism's remains decompose and leave behind a hollow impression in the sediment. This impression reflects the organism's structure. If the hollow space later fills with minerals or other sediments and hardens, it becomes a cast fossil, which represents the original shape of the organism. Both types of fossils provide valuable information about past life and environments.