tissue

Maudi

probably gona be a very simple answer but here goes...we have fossils....casts of bones of creatures that lived millions of years ago....but no soft tissue..skin..fur...scales...liver.heart...muscle..soft tissue fossils....but yet we have plant fossils...leafs .ferns etc...how come?

El Siglo

Because the soft tissue is destroyed by microbial processes whereas the tougher material becomes petrified. Bacteria will break down the most degradable material and whatever is left over will be buried by sediment. Plants tend to be tougher than soft tissue, lignin and cellular walls are harder to break down, hence why they're usually petrified.

slowburner

Just to add that the internal organs of animals are host to all sorts of bacteria which cause no harm - while the animal is alive.
When the animal dies, the animals' defence system is switched off, bacteria multiply and begin to consume the soft tissue.
That's why taxidermists and the ancient Egyptians removed the internal organs.
How much soft tissue is preserved or petrified is also affected by the pH of the surrounding soil conditions, and the circumstances in which the plant/animal became entrapped.
'Bog bodies' for example, are remarkably well preserved because of the anaerobic/highly acid conditions of the bog which reduce bacterial action.
Conversely, bodies buried in soil with a low pH and exposed to air, will have a very high rate of decomposition - so much so, that even bones may be completely decomposed.