Earliest known Chordate: Cathaymyrus diadexus

Cathaymyrus, the fossil on the left, is about one inch long. It was found recently in the Changjieng fossil beds in southern China which are dated at 535 Ma. It is about 10 million years older than Pikaia, shown on the right.

These animals are believed to be the earliest ancestor of animals with backbones. They were free swimmers. There are not many of these kinds of animals in Cambrian fossil sites because they didn't live in the substrate.

Cathaymyrus photo from Earth Magazine, April, 1997
Pikaia, detail of painting by Christopher A. Klein