The answer is hard tissue.
Usually, hard tissue, such as bones and teeth or exoskeleton is much more preserved than soft tissue (organs, skin, etc.). Fossils become fossils by a process of mineralization. Hard tissues are more mineralized during life than organs. So it is no surprise that hard tissues take part in the process of mineralization and is preserved in fossils, unlike soft tissues.
Energy convention: Convection is the motion of a fluid driven by temperature differences across that fluid. When a fluid is heated, the region in closest contact with the heat source becomes less dense due to increased kinetic energy in the particles. Convection is one of the fundamental ways that heat is transferred
Starfish has a endoskeleton
a coral has a exoskeleton
sponge has neither
