This topic has been discussed to death in various arenas, but I feel nobody has really talked about it or looked at the options.
First a bit of background. People have created various ‘animals’ but these are just clever (and not so clever) hacks. Some clone the flamingo and create farm animals, others clone the aquarium or guinea pig to create dogs and cats. Sorry, this just doesn’t cut it. It’s not really a pet and even though you can ‘play’ with it, it’s not real. So what makes a real pet? Something that will follow you around, go anywhere on its own, etc. etc. In other words, be sentient and real. Can this be accomplished? According to Maxis, no, however I think otherwise.
Maxis says their engine doesn’t support non-bipedal animations. However, knowing what I think I know about the system, I disagree. A CMX file is composed of 3 sections, the skeleton (bones) of a character, the suit (mesh) of the character and the skills (animations). So if you were to create brand new bones, suits and animations, I think the system could support it. It doesn’t look specifically for legs or anything else to animate. It just looks for whatever animation information there is in the CMX and CFP file (telling it the translations/rotations) and executes it. So I don’t see why a correctly defined 4 legged beast wouldn’t work (of course, making all the animations and whatnot is a feat in itself, but that’s just time and effort).
Of course, the hard part is having The Sims recognize them. The problem is that somewhere I believe The Sims is hard coded to use either an adult or child skeleton (at least that’s the way it is in SimShow and probably Character Makeover). I don’t think you can define new ones. So if you don’t mind all of your Sim children to become puppies (maybe not a bad idea except for the mess) then it might work. Otherwise, I don’t think they can be recognized. For a permant fixture, this would necessitate the addition of a new designation (a=adult, c=child, p=pet) and the appropriate animations setup (p2o=pet to object, p2a=pet to adult, etc.) I’m currently talking to a few people at Maxis and elsewhere to see about how real this could get and building a “Pet” version of SimShow to see if it can be done using a cat from Poser for my mesh and animation. I’ll post the results here when I have something to show.