Life › The Cambrian explosion › Burgess Shale (Canada)
Pikaia
c. 508 million years ago· Fossil or site· Animals
Well establishedStrong fossil, genetic or geological evidence.
A small, eel-like animal from the Burgess Shale and one of the earliest known chordates, the group that includes vertebrates.
See it on the Life map →What happened
About 4–6 cm long, Pikaia gracilens was first described by Charles Walcott in 1911 as a worm. In 1979 Simon Conway Morris recognized chordate features: a stiffening rod (notochord) and repeated blocks of muscle along the body, like a modern lancelet. It had a small head with two tentacles and probably swam by flexing side to side. A 2024 restudy argued earlier reconstructions showed it upside down.
Why it matters
Gould used it as a stand-in for our earliest ancestor; it shows the basic body plan shared by all chordates, including vertebrates.
The evidence (fossils, genes, rocks)
More than 100 Burgess Shale specimens, described in detail by Simon Conway Morris and Jean-Bernard Caron in 2012 and reexamined in 2024.
Still debated
Exactly where it sits on the chordate family tree, and whether its odd head features are primitive or specialized, remains debated.
Connections (2)
▸Burgess Shale (Canada) preserves PikaiaWell established
The connection
Pikaia had no bones, shells or teeth, so it survives only where rock preserved soft tissue. The Burgess Shale mudflows captured its notochord and muscle blocks as faint dark films, enough to recognize it as one of the earliest known chordates.
When and how
Walcott Quarry, Yoho National Park, British Columbia, about 508 million years ago; named by Charles Walcott in 1911.
The evidence
More than 100 specimens; chordate features visible under magnification and angled lighting, confirmed by Conway Morris and Caron in 2012.
Debates and open questions
Some features, such as its unusual head and a long structure along its body, have been read very differently, including a 2024 claim it was drawn upside down.
▸Pikaia is a chordate cousin of First vertebrates: jawless fishStrong evidence
The connection
Pikaia and the first vertebrates share the chordate body plan: a notochord stiffening the back, blocks of muscle for swimming, and a nerve cord along the back. But Pikaia lacked the clear skull, eyes and gill structures of Haikouichthys, and it is younger, so it is a side branch, not an ancestor.
When and how
Burgess Shale, Canada (Pikaia, about 508 million years ago) and Chengjiang, China (first vertebrates, about 518 million years ago).
How sure are we?
Comparisons of the fossils with living lancelets and lampreys; family-tree analyses place Pikaia near the base of the chordates.
Debates and open questions
Whether Pikaia is closer to vertebrates, to lancelets, or sits outside both depends on how its strange head features are interpreted.