The Burgess Shale fossil commonly identified as an early known chordate is Pikaia.
Pikaia gracilens lived in the Middle Cambrian, roughly 505 million years ago, in what is now British Columbia, Canada. Its fossils come from the Burgess Shale, a deposit famous for preserving soft-bodied organisms from the Cambrian explosion. Pikaia had a slender, laterally compressed body and appears to have moved through the water with eel-like swimming motions.
The fossil was described by Charles Doolittle Walcott in 1911, who initially classified it as an annelid worm because of its body segmentation. Later examinations by Harry Whittington and Simon Conway Morris identified features interpreted as a notochord and segmented muscle blocks—key chordate characteristics. Chordates include tunicates, lancelets, and vertebrates such as humans.
Pikaia is often described too strongly as the direct ancestor of all vertebrates or of humans. The fossil demonstrates that chordate-like animals existed during the Cambrian, but its exact position on the chordate family tree remains uncertain. It is best treated as an early chordate, not a confirmed direct ancestor.