One reason why most fossilized animals have incomplete remains is that parts like the:

The Skin weren’t preserved at all

Explanation:

One reason why most fossilized animals have incomplete remains is that parts like the skin aren't usually preserved at all. There are however some instances in which the skin are preserved but it’s very rare.

This is because of the action of decomposers on the remains of the body parts and the presence of scavengers which eats the body parts thereby making the remains incomplete.

its temperature is increasing. this causes molecular vibrations to increase.