The appendix is a vestigial structure in all vertebrates

The claim states two things: that the appendix is vestigial, and that this applies to all vertebrates. First, modern biology recognizes that the human appendix has important immune functions (e.g., housing gut flora), making it not entirely vestigial. Second, not all vertebrates even possess an appendix; the vermiform appendix is mostly found in select mammals (such as primates, wombats, and rodents), making the claim factually incorrect across vertebrates. Papers [2] and [3] support the notion that structures traditionally labeled as vestigial actually maintain functional relevance.