These are people who have the souls of sentient races put into the bodies of animals by Edmus Sablefane. They all have a gem under their chin which glows and projects speech. When someone is changed into an alter animal, their age is retained. So if a child is changed into a cat they will become a kitten. Alter animals are unable to reproduce.
To change back their soul needs to be taken from the stone an put into another body, or the entire stone can be moved to the chin of another body (animal or other sentient race) to effectively make an alter sentient creature.
Also, just as a courtesy in case the party tries to change people back, all alter animals should have a pre-change page.
AA = alter animal version of person
PAA = pre alter animal version of person