Why is it difficult to fossilize large animals? There are not enough rocks to cover large animals.
Large animals are harder to cover due to many environmental factors.
Large animals are usually decomposed faster than smaller animals.
Fossilization requires very specific environmental conditions.

The hard parts of organisms, such as bones, shells, and teeth have a better chance of becoming fossils than do softer parts. One reason for this is that scavengers generally do not eat these parts. Hard parts also decay more slowly than soft parts, giving more time for them to be buried.

Explanation:

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

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