A fossil shell is filled with mud.The shell dissolves, leaving an impression of its inside surface on the shell-filling lump of mudstone.What type of fossil is this?

Question

Quizplus · Accepted Answer

The impression of the inside surface of the shell is called an internal mould. This type of fossil forms when a shell, bone, or other hard part is buried in sediment, and the sediment later hardens into rock. The original hard part dissolves or decays, leaving a cavity, or mould, in the rock that is a mirror image of the organism's internal shape.

A Fossil Shell Is Filled with Mud