How about the piano-bass-guitar trio? Did it start with Tatum? That seemed to be the more dominant format until bop, and it lived on well into the fifties, especially in lounge combos (as seen in many films).
Edit: Ah, I took a look at that Ned Judy page. So this format started with Clarence Profit, according to him, a name I didn't know. I also didn't know or remember that King Cole's trio predates Tatum's.