Below is my hand placed on one of these monster 'shrooms. This would make quite a meal. They are edible, but from what I read, they are not super tasty. Hmmm, maybe if they were dipped in chocolate....
There are many fungi considered shelf or bracket fungi. This one is Polyporus squamosus. It has a couple of common names. One is Dryad's Saddle and another is Pheasant's Back.
So what in the world is a Dryad and why would it have a saddle? Well, a Dryad is a tree nymph. And if you eat some of the other mushrooms that you shouldn't, you will probably see them riding on this saddle-shaped mushroom. :)
The top of this fungus is scaly, covered in squamules. And this is where the squamosus name fits in. The pattern on the top of the fungi are very similar to a female pheasant's back. This is why the other common name for these fungi are Pheasant Backs. Supposedly, many a hunter have snuck up on these fungi when they are located low on a trunk or on a downed log, thinking they have located a resting pheasant.
Mushrooms in the genus Polyporus are stalked, as you can see in the above photo. Polyporus means "many pores". Some fungi have gills, or lamellae, and some, like these, have pores that contain all the tiny spores. The spores act similar to seeds of a plant. Below is a bottom shot showing the pores.
Below is a close-up of the pores. A fungus this size could hold billions of spores. The spores are so minute that they can be carried miles up into the atmosphere and deposited thousands of miles away.
If these spores land on a tree or downed log, they will produce enzymes that break down the wood, releasing the nutrients and minerals to be used by other forest organisms. The enzymes specifically break down lignin, or the brown hard part of the wood. They make the wood so that it appears spongy and moist.
If you want to learn more about these fascinating mushrooms and all about polypores go to Tom Volk's site. He is a professor from the University of Wisconsin-La Crosse. He has a great writing style, is very informative, and is pretty funny at times.