Final answer:
The tailbone is known as the coccyx, which is at the end of the vertebral column and is a small bone formed by the fusion of four coccygeal vertebrae.
Step-by-step explanation:
The part of the spine referred to as the tailbone is the coccyx. The coccyx is a small bone located at the inferior end of the adult vertebral column. It is formed by the fusion of four coccygeal vertebrae. This fusion starts around age 20 and is usually completed by middle age. While it does not bear weight when standing, it can receive some of the body's weight during sitting.
Our possession of a coccyx, or tailbone, despite the absence of a tail, supports the theory of evolution, suggesting that our ancient ancestors did have tails. The vertebral column as a whole evolves from 33 vertebrae to eventually include the 24 vertebrae of the cervical, thoracic, and lumbar regions, plus the sacrum and coccyx.
The vertebral column consists of distinct regions that serve various functions, with the coccyx being the terminal section, serving as a vestigial remnant of a tail that exists due to our evolutionary history.