Well, I think it's implied that it is a singular shingashong in the story itself. Not to mention that, as far as I know, we've never seen two in the same drawing. So I don't think anyone has even toyed with the notion that Shingashong is a breed of mutant yukkuri.
Oh, and for this picture I assume it's the same one being fed, playing and sleeping during different intervals, just showing the same one doing each action.