Why would you be unlikely to find a notochord in an adult chordate?

In adult chordates, the notochord is typically replaced by the vertebral column (spine) during development, providing a more rigid structure for support and movement. While some primitive chordates retain the notochord throughout their life, most vertebrates exhibit a transition to a bony or cartilaginous backbone, which serves similar functions but offers greater protection and strength. Consequently, the notochord is usually only present in the embryonic stages or in specific chordate groups that do not develop a backbone.