Carbonized remains are thin, approximately two-dimensional films of carbon preserved on a flat surface of rock. They are most often black in color, reflecting the fact that they composed mostly of carbon (as is coal, which is also black in color). Most fossils that exhibit “soft part” preservation are carbonizations.
I would say the answer is the Carbon remains of the original organism.
I think the answer you're looking for in theory but I could be not understanding the question well enough.
Answer:
Because the carbon atom is just the right, small size to fit in comfortably as parts of very large molecules.
Explanation:
Carbon atom can form four chemical bonds to other atoms.
I believe it would be The muscular system