Yes, GGfS, I will readily concede that point: The Beatles answered the question "Where could music possibly go next?" Their roots were in American Rock 'n Roll but they spawned an explosion that is still ongoing. Imitators and the truly inspired took off in a myriad of directions in ways that seemed inconceivable before their advent.

I would argue that the Moody Blues' Days of Future Past was a really gigantic leap also: something more than three guitars and a drum set. It demonstrated that Rock and Pop were more than kids' stuff. Rock began to grow up.