:p:

The Thom yelps in Climbing Up The Walls are pretty epic.

Fortune Teller-Hot Cross is the first screamo song I remember really liking.

Refused were the first I heard

The Beatles screamed in Helter Skelter and Why Don't We Do It On The Road.

I feel that I might be wrong with this, but bands like Slayer had allot to do with it. More so Pantera though (starting with Cowboys From Hell that is, not the glam era with Terry and Power Metal with Phil) Like if you look up "I'm Broken" for example or "This Love" or "Cowboys From Hell" you'll hear much of the screaming and growling you're probably looking for.

wut.
Radiohead came around in 1985, Rites of Spring formed in 1984. If you think of screaming as a vocal technique in a general sense, I say Little Richard did a pretty good job at screaming his butt off. That was in the '50s. The Beatles screamed in Why Don't We Do it In the Road and Helter Skelter (as previously mentioned), and some thrash metal or early black metal bands must have been screamin' and growlin' before 1984.

The earliest I band I can think of to do stereotypical screaming is Cromagon.

That was... unusual. And it's from 1969?

Yep. Beats out most other screaming by several decades