Querry about the Coccyx.

I would like to ask a couple of questions regarding the vestigial strucure known as the Coccyx. Some people deny its vestigiality arguing that it serves as an anchor point of nine - 9 - muscles. My questions are:

1) How do these 9 muscles and their functions compare to the muscles attached on the tailbone of caudate animals? For example (please correct me if I'm wrong!): One of the 9 muscles attached on the human Coccyx is the Levator Ani muscle, which in caudate animals serves to the motion of the tail, whereas in humans it plays a role in defecation. It stroke me though noticing more than one of the cats that live in my garden moving their tail like the handle of a pump while defecating, which means (my guess!) that the levator's role in that function exists in caudate anumals as well.

2) Is it possible that some of those 9 attachments are themselves vestigial? For example: One of the 9 muscles attached on the Coccyx is Gluteus Maximus, the largest and most massive muscle of the human body. To the best of my knowledge (once again: Please correct me if I am wrong!) this muscle is mainly attached to the Saccrum, whereas there is only a minute attachment to the Coccyx, which I wonder whether it is of any function at all or not. Indeed, the Gluteus Maximus is not only a very large and massive muscle, but it also serves in stabilizing the torso in the upright position. How could such a function of such a muscle receive any service at all from its minute attachment to such a frail and (if I am not mistaken!) inappropriate structure as the Coccyx (4 tiny vertebrae instead of a rigid formation)?

Could anyone suggest any references that deal with the above topics?