Pikaia is most primitive vertebrate known

 

Yesterday I was talking to one of my colleagues and she asked me if I'd heard the latest news about the Burgess Shale. I confessed ignorance so she told me that scientists had just discovered a primitive vertebrate fossil in the Burgess Shale.

Hmmm ... I was aware of possible primitive vertebrates ("Craniates" is a better term) in the deposits from China (e.g. Myllokunmingia) but I'd never heard of a vertebrate fossil in the Burgess Shale so I thought I'd check out the press release.

It's from my university!!! [Pikaia is most primitive vertebrate known]

Researchers from the University of Toronto, the Royal Ontario Museum (ROM) and the University of Cambridge have confirmed that a 505 million-year-old creature, found only in the Burgess Shale fossil beds in Canada’s Yoho National Park, is the most primitive known vertebrate and therefore the ancestor of all descendant vertebrates, including humans.

The research team’s analysis proves the extinct Pikaia gracilens is the most primitive member of the chordate family, the group of animals that today includes fish, amphibians, birds, reptiles and mammals. Their study is based on the analysis of 114 specimens and is published in the British scientific journal Biological Reviews.

The headline is wrong. Pikaia is a chordate but not a vertebrate as the quotations from the researchers make clear. The press release from Cambridge is only a bit better [Humans' ancient ancestor revealed - as a 505 million-year-old 'eel']

“The discovery of myomeres is the smoking gun that we have long been seeking,” said the study’s lead author, Professor Simon Conway Morris of the University of Cambridge. “Now with myomeres, a nerve chord, a notochord and a vascular system all identified, this study clearly places Pikaia as the planet’s most primitive chordate. So, next time we put the family photograph on the mantle-piece, there in the background will be Pikaia."

Furthermore, this really isn't news. Pikaia was featured in Stephen Jay Gould's book Wonderful Life published in 1989. Even then, Pikaia gracilens was thought to be a chordate similar in broad features to the cephalochordate (non-vertebrate chordate) Amphioxus. This classification was attributed to Simon Conway Morris in 1979. The Wikipedia article [Pikaia] points out that this classification was not universally accepted.

The important points are: (1) that Pikaia is a primitive chordate but not a primitive vertebrate and the press release is just dead wrong about that and, (2) this is old news.

BTW, is Conway-Morris right about Pikaia being the oldest chordate? I thought the fossils from China were older and some of those might even be vertebrates. If that's true then Pikaia lived after the divergence of cephalochordates and vertebrates and it's not even remotely possible that it's our ancestor.

There ought to be a new rule about press releases. Each one should have a statement at the end saying the the press release has been read by the authors of the study and they approve its content.

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Conway Morris, S. and Caron, J-B (2012) Pikaia gracilens Walcott, a stem-group chordate from the Middle Cambrian of British Columbia. Biological Reviews. Article first published online: 4 MAR 2012 [doi: 10.1111/j.1469-185X.2012.00220.x]