a bacon

greatest animal ever invented

A golden retriever.

I'd take it into work and have it run around my desk, and I'd have a matchbox for it to sleep in.

An enormous ant.
Or a giant mouse.

thylacine

Most of my favourite animals are pretty much pocket-sized anyway (robin, Pekin robin, pipistrelle bat, hamster, squirrel &c).

So from larger things, I think perhaps a porcupine, as they are beautiful, although some sort of reinforced pocket may be neccessary. Or maybe a donkey.

I have some short porcupine spines which I keep meaning to frame or something.