Was the Tailbone a Tail?

The coccyx is a triangular arrangement of bone that makes up the very bottom portion of the spine below the sacrum. It represents a vestigial tail, hence the common term tailbone.

Why do humans have a tailbone but no tail?

The tail vanishes by the time humans are born, and the remaining vertebrae merge to form the coccyx, or tailbone. Tailbones helped our ancestors with mobility and balance, but the tail shrank as humans learned to walk upright.

Is the coccyx a vestigial tail?

In tailless primates (e.g. humans and other great apes) since Nacholapithecus (a Miocene hominoid), the coccyx is the remnant of a vestigial tail. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan.