Proto-Progressive Rock bands

As it's name clearly indicates, Proto-Progressive Rock refers to the earliest form of progressive rock or progressive rock in embryonary state. The Proto-Prog bands normally were formed and released albums before prog rock had completely developed, but there are some rare Proto Prog bands from the early 70's as well, because the genre didn't expanded to all the continents simultaneously. The common elements in all these bands is that they developed one or more elements of prog, and even when not completely defined as part of the genre, they are an important stage in the evolution of progressive rock. Read more here.