I'm going to guess the v/illagers. Something seems to have happened to split them into the monkish villagers and the lavish, magic-using illagers. (And the solitary witches.) Perhaps at one point they were a much wider-ranging culture.
Though, interestingly, villager zombies are distinct from regular zombies. Where do the regular zombies come from? They can't all be dead Steves and Alexes, can they?
Oh, and right - I forgot the icebergs. Though frankly they don't seem that interesting, except maybe as a source for packed ice.