Answer:
They are fossil "clues." they are the structures preserved in sedimentary rocks that record biological activity. They are the traces that an organism leaves on its way of life and behavior. They are the traces of organic activity such as footsteps, fecal waste or signs of predation. Cavities, grooves or perforations are traces, they can be in the sediment. When these traces are covered by a sheet of sediment, it slides through cavities and depressions forming a mold of the original footprint.