There was a fox wondering when a snake bite him. Poison entered his blood flow, killing him!
The archaeologist found and dug up the fossil! He will now explain why only sedimentary rock covers the fossil and why not all living things get fossilized.
He turned into bones...
The fox eventually became covered in silt.
...Until you can't see the bones anymore
Underneath, the fox's soft tissues decompose leaving hard bones or rock behind.
Sedimentary rock is the only rock that does not crush and break fossils, plus, it is what covers fossils. Also, if an organism decomposes or gets eaten it can't become a fossil, which explains why fossils are more rare.