Did you know that cats share a distant ancestor with weasels? Evolution is a complex thing, full of dead ends and surprises. Survival of those who best fit their niche and extinction of other dominant species can lead to a family of animals to explode into dominance or fade to obscurity. So let's start with the common household cat. How might they have evolved differently on your world or how might they change if transplanted to your world? What would happen if they were subjected to your world's magic, radiation, or wilds? Would they have died out millennia ago? Would they be so different they were unrecognizable?