Answer:
A hollow space that was once occupied by a dead organism is a:
mold fossil
Step-by-step explanation:
In this type of fossil there are not parts of the animal itself, but we can see an impression of its body, for example a dinosaur footprint. Mold may later be filled with other sediment or minerals precipitated from groundwater, making a cast of the fossil. A mold forms with animal remains, the hard parts of the organism get buried in sand or clay and next they decay and dissolve.