Amphioxus’ body plan shows what a vertebrate’s ancestor might have looked like with a nerve cord, a brain, gill slits, segmented muscles and a notochord that would become the discs in the backbone.
Chordate Animation: Amphioxus to Vertebrate Body Plan
Next Generation Science Standards for this Video
An animal like Amphioxus was the ancestor of all vertebrates, possessing key features all vetebrates have today. It was quite an evolutionary trip to go from a tiny worm-like animal to an elephant.