Unless, of course, it is a jellyfish, with no hard parts. Casts of soft creatures are truly rare. On the whole planet, there are only a dozen-odd important deposits showing the shapes of soft life forms. We only find insect fossils in these deposits, and in amber . Next, there's the issue of scavengers and rot.
Forests have both, plus forests tend to have acidic soil.
So, most of our fossils of forest dwellers are because they foolishly tried to ford a raging river. You may have seen nature films on TV of herds of caribou or wildebeeste doing just that. But only animals big enough to migrate try to ford rivers. Foxes and squirrels don't migrate. So, the fossil record of forest dwellers is absolutely terrible, and highly biased towards big herd animals.