The rats in question were a weird byproduct of Rex rats. See, my stepmother figured that since they were breeding rats anyway--to feed the snakes, and later on quite a large scale to sell to pet stores--they might as well do rat shows, and to that end bred some lovely show rats with the unusual markings and so forth. (Before you say anything, yes, I do know how weird this sounds.) And one of the types of interesting rats is the Rex rat, which like a Rex cat has tight, kinky fur. Fine and good so far. Problem is that the gene appears to be one of those weird recessives that double up poorly--carry one gene for sickle-cell anemia and you're malaria resistant, carry two and you die young. In this case, one Rex parent gets you a Rex rat, two Rex parents get you a naked rat with fur on its head and in an extended mohawk down the spine, and bald pink skin everywhere else.
They were pretty funky lookin' little rats. And the rat in my quick scribble does, indeed, somewhat resemble them in its bony weirdness. Obviously that particular image stuck somewhere in the art brain and was just waiting for a chance to re-emerge.