Discern Shapechanger

With a standard action spent in concentration, you can see the true form of polymorphed, disguised, or transmuted creatures within 60 feet. Each round, you can examine one creature you can see and determine whether it is polymorphed, disguised, or transmuted, and what its true form is.

If you look at a shapechanger in its true form, you know that it is a shapechanger, but cannot determine what other forms it might be capable of assuming. For purposes of this spell, a shapechanger is any creature with the shapechanger type or a supernatural or extraordinary ability that allows it to assume an alternate form. A wu jen who knows polymorph self is not a shape- changer (since a spell is not a supernatural or extraordinary ability), but a spirit centipede is (since it has the exceptional ability to assume alternate forms, though its type is outsider).