What anatomical structure defines vipers as members of Phylum Chordata?

Answer

Notochord

Members of the phylum Chordata possess a notochord at some point during their development. In the evolutionary lineage of snakes, this cartilaginous rod has evolved into the vertebral column, or backbone, which provides essential structural support for the body.

What anatomical structure defines vipers as members of Phylum Chordata?
classificationreptileserpentviper