The Crazy HR wrote:Every one of them. They were inbetweeners in the studio back in early 40s (Halpern is seen in the 1940 WB Christmas reel). Matz was the first one to get promoted. His first credit was on "Three Little Bops" (1957), but I don't think he did any animation in that short. He became a full animator on theatrical shorts in 1961, after Art Davis left, but he was an animator prior to that on "The Bugs Bunny Show" (when Davis was still there). Art Leonardi and Lee Halpern were promoted to animators a short time after Davis left (their first credit was on "The Last Hungry Cat"). I think some of the assistants were promoted to animators later at DFE.
When Tiny Toon Adventures was starting I read that Leonardi joined Warner's in 1957 and was first assigned to McKimson's unit.