I honestly have no skin in the game re the Fire starters=Chinese Zodiac theory
The only time I ever think about this is when someone brings it up which is not often. I've broken off from it, but each their own. All I will say is that maybe, if Pokemon series goes on for a long time, the Fire Starters (or at least the Fire-Type) will indeed have a representative for each Pokemon in the Chinese Zodiac (and maybe some of its variations as well). Will it be within the first 12? As I said, I doubt it at this point, you have to do some major jumps in conclusions to make it work now, but who's to say if the series goes onto 15, 17, or 20 gens they won't include a more rodent-like one, or a fire snake, a fire horse unique from the Kanto Ponyta family, etc..
Veering slightly into wishlisting but my longstanding idea for an ox-based fire starter would be one that starts out as a foal with extremely small shaky legs and gradually gets bigger, thicker, and more aggressive, perhaps growing flaming horns and utilising various kicking moves.
Though that could also work for a horse, given that that's one of the remaining animals according to the zodiac theory. Though there's obviously overlap with Rapidash there, so I think a pegasus (with flaming wings) would be a great fresh concept to explore.
Wouldn't mind if it was a Muskox (yes, I know they're not oxen by genetics, but in Pokemon that doesn't matter). As for a horse different from the Ponyta family, maybe they could base it on the horses which pulled early Firefighting carriages which were often called "Fire Horses".
Always a fun fact to bring up - Crocodiles/Alligators/Caimans/Gharials are more closely related to Birds than other reptiles.
So what you're saying is Skeledirge is the dragon (cause they're an archosaur, cousins of dinosaurs, and dino=dragon) and Charmander is the snake (cause European dragon = serpent/wyrm).