Researchers at the Royal Ontario Museum and the University of Toronto have described an exceptionally well-preserved new fossil species of bristle worm called Kootenayscolex barbarensis. Discovered from the 508-million-year-old Marble Canyon fossil site in the Burgess Shale in Kootenay National Park, British Columbia, the new species helps rewrite our understanding of the origin of the head in annelids, a highly diverse group of animals which includes today’s leeches and earthworms. This research was published today in the journal Current Biology in the article “A New Burgess Shale Polychaete and the Origin of the Annelid Head Revisited.”
One key feature of the new Burgess Shale worm Kootenayscolex barbarensis is the presence of hair-sized bristles called chaetae on the head which led Nanglu and Caron to propose a new hypothesis regarding the early evolution of the head in annelids. “Like other bristle worms, Kootenayscolex possesses paired bundles of hair-sized bristles spread along the body; this is in fact one of the diagnostic features of this group of animals,” Nanglu added. “However, unlike any living forms, these bristles were also partially covering the head, more specifically surrounding the mouth. This new fossil species seems to suggest that the annelid head evolved from posterior body segments which had pair bundles of bristles, a hypothesis supported by the developmental biology of many modern annelid species.” Paper. [access] – Karma Nanglu et al. A New Burgess Shale Polychaete and the Origin of the Annelid Head Revisited. Current Biology, 2017 DOI: 10.1016/j.cub.2017.12.019
From Colette Derworis at CTV:
Nanglu said Kootenayscolex barbarensis is unlike any other bristle worm that’s been studied due to its more complex head.
“Previously all of the Burgess Shale (bristle worms) were thought to have a relatively simple head,” he said. “It’s pretty much similar to the pattern that we would expect if you look at the modern forms and try to trace back what their early ancestor might have looked like.
So the complex head has been around longer than we thought.
Many good illustrations here (Royal Ontario Museum)
See also: Treasure trove of new Cambrian fossils raises big question. And if the Cambrian non-shelly animals turn out to be as complex as the non-shelly animals today… ? Then where, how and what is the evolution?
Stasis: Life goes on but evolution does not happen