Oh, I'm wrong--casters with spells that enable them to change shape can apparently take the class also. Here's the full list from the manual:
Special: You must be able to assume an alternate form. See the following list:
Arcane or divine classes with the ability to cast Polymorph Self.This includes:
Archivist (spell level 4, class level 7)
Hexblade (spell level 4, class level 14)
Ranger (spell level 4, class level 15)
Shaman (spell level 4, class level 7)
Sublime Chord (spell level 4)
Sorcerer (spell level 4, class level
Suel Archanamach (spell level 4, class level
Witch (spell level 4, class level
Wizard (spell level 4, class level 7)
Divine classes having the Animal domain, which gives the ability to cast Shapechange at spell level 9.
Classes with the ability to use one of these invocations:
Mask of Flesh, Humanoid Shape, Spider Shape, Hellspawned Grace.
Classes with certain special abilities:
Bonded Summoner: Elemental Form (Level 10)
Druid: Wild Shape (Level 5)
Initiate of Draconic Mysteries: Dragon Shape (Level 10)
Ninja Spy: Thousand Faces (Level 7)
Werewolf: Alternate Form, Wolf (Level 1)
Certain races:
Changeling
Fey'ri
Hound Archon
Irda
Naztharune Rakshasa
Pixie,
Rakshasa
Shifter
Yuan-ti Pureblood
Zakya Rakshasa