I thought that was a cover?
Go figure.
@WingnutNope. One of the original guitarists that wrote it was playing lead. Maybe even some of the other guys were original players,too. There are a bunch of live covers of it by both original guitarists all over ebay,but the fat guy playing lead wasn't fat back then so you may have a hard time recognizing him.
I do think mushrooms should get co-writing credit,but I may be wrong.