19. Another interesting fact about the human tailbone is that it is considered to be the remnants of which physiological feature that apparently humans once possessed?
From Quiz Tales About Tails
Answer:
Vestigial tail
Apparently our tails, if you believe we're descended from apes, are the remnant of somewhat longer tails all our far distant ancestors once possessed. All mammals possess a tail, some with more tail than others. During the first stage of a newly created embryo's development in the womb, at approximately one month old, this tail can still be clearly seen for a period of four weeks or so. Its original purpose for early humans was to help with mobility, but, as this is no longer a necessity with modern man, the tail very, very rarely develops any further. Occasionally, in genetic defects present at birth for some little babies, this vestigial tail however can still appear.