Back in the 1940’s, animation director Bob Clampett (director of Bugs Bunny and creator of Beany and Cecil) proposed a series of animated theatrical shorts adapting the John Carter of Mars books by Edgar Rice Burroughs (creator of Tarzan). This footage was the test reel for the studios. Apparently one major hollywood studio was interested in producing these shorts, but changed their mind when they thought the concept might be to weird for some people.
It’s to bad they never got made. Who knows what direction animation might have taken if they had.