[fidelis]

Understood. There is also room to argue whether ballad singers and do-wop should be in the mix. Many of the forms that became popular in the 50s were seen at the time as efforts by the music industry to tame ‘rock ‘n roll.’ I know ‘skiffle’ in the UK was seen that way.

That is true. Sometimes, in the history of rock & roll, people either like to draw distinct categories or see it more as a development with some artists more or less sticking to distinct styles within that development. For example, early 50's artists like Huey Smith and Big Joe Turner are commonly considered to be R&B artists, but at the same time many others recognize them as being highly influential to roots rock & roll. Listening to their music, one could easily categorize them with Little Richard and Chuck Berry, recognized Rock & Rollers.

[shadowlands1960]

Or the King Daddy of them all... Muddy Waters.... almost universally seen as Chicago blues.. but his ‘Mannish Boy’ was arguably the first recognizable rock song. His decision to ‘plug in’ the blues was decisive for music in the 50s.