Why do scientists disagree about whether Yunnanozoon lividum was a chordate?

Scientists disagree about whether Yunnanozoon lividum should be classified as a chordate primarily because of the challenges associated with interpreting the anatomy of very early, soft-bodied fossils.1

Dating back approximately 530 million years, Yunnanozoon lividum—along with the related Haikouella—possesses several features that are characteristic of chordates. However, because these organisms predate the more established fossil record of later, clearly defined chordates like Pikaia gracilens, their exact evolutionary placement remains a subject of debate among paleontologists. The ambiguity arises from the difficulty in definitively identifying the full suite of diagnostic chordate traits—such as a notochord, dorsal nerve cord, and specific pharyngeal structures—within these ancient, poorly preserved specimens.12