So, the way I see it, the rules for both Pathfinder and 3.5 say you can't make a familiar out of your animal companion, but neither of which state that you can't make an animal companion out of your familiar... I haven't found anything in the rules of either system that states an animal companion has to be an unmodified creature.
Now I have a house rule that states Barbarians and Sorcerers are "wild" classes, and as such must be picked as your first class if you're going to multiclass as one of them. This leads to my question:
If you are a Sorcerer first and have a familiar, and then take a level in Druid with an animal companion, since originally the familiar wasn't modified before becoming a familiar, would it then be acceptable to make your familiar an animal companion AFTER its already your familiar thus becoming a familiar animal companion?