True, that we can find such things Walrus. However, most living things will leave no trace several million years down the line. Should we dig up the entire planet to attempt the impossible task of the perfect puzzle? You have to operate within reasonable parameters. Most actual will simply break down within a relatively short space of time. Thus you are lucky to have the records that we do. We see them weaken in our own lifetimes within our bodies. It only accelerates post death with nothing to feed them.