Final answer:
A mold fossil is the type that leaves an open space in a rock left by a decaying organism. It captures the shape and detailing of the organism. If it gets filled with sediments it becomes a cast.
Step-by-step explanation:
The fossil type that is an open space left inside a rock by an organism that has decayed is called a mold fossil. When the organism decays, it leaves a cavity in the sediments around it, which captures the shape and surface markings of the organism. This cavity, or mold, is then often filled with sediments or minerals to create a cast. However, if it remains unfilled, it is recognized as a mold fossil. Such fossil types help in understanding the external anatomy of ancient organisms in detailed manner.
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