The researchers think that Cathaymyrus , like Pikaia , is a fossil relative of modern lancelets. Chordates are usually long and narrow, with a stiffening rod of cartilage running along the back. In vertebrates this rod, the notochord, is replaced by bone to become the spinal column. In other chordates, such as sea-squirts, the notochord is present only in the larva. Adult sea-squirts have no notochords.
Lancelets are somewhere in between, with a notochord that remains throughout life.
There is good evidence that Cathaymyrus and Pikaia had notochords. But the matter is more debatable for the strange fossil Yunnanozoon , also from Chengjiang. Some researchers think that Yunnanozoon represents a whole group of extinct chordates. Dr Shu and colleagues disagree, placing it among distant relatives of chordates called hemichordates. Chordates have other defining features.