These fossils are highly significant because they imply the contemporary existence of the tunicates and craniates in the Early Cambrian during the so-called Cambrian Explosion of animal life. In the Tree of Life project, conodonts are placed as a subgroup of vertebrates . Chordates other than craniates include entirely aquatic forms. The strictly marine Urochordata or Tunicata are commonly known as tunicates, sea squirts, and salps. Nearly all are sessile as adults but they have free-swimming, active larval forms.
Urochordates are unknown as fossils.
Cephalochordata are also known as amphioxus and lancelets. The group contains only about 20 species of sand-burrowing marine creatures. Yunnanozoon and Pikaia are likely related to modern cephalochordates. These are the earliest known members of Vertebrata, the chordate subgroup that is most familiar to us. The notochord is an elongate, rod-like, skeletal structure dorsal to the gut tube and ventral to the nerve cord.