Is a post-anal tail a vertebrate?

A post-anal tail is not a vertebrate itself; rather, it is a feature found in certain vertebrates, including all chordates during some stage of their development. This tail extends beyond the anus and is characteristic of the embryonic stages of vertebrates like mammals, birds, and fish. In some species, the post-anal tail is retained into adulthood, while in others, it is lost during development. Thus, while vertebrates can possess a post-anal tail, the tail itself is not classified as a vertebrate.