Kootenayscolex barbarensis: Cambrian Period Worm Had Hair-Sized Bristles on Its Head and Body
A new species of bristle worm that lived about 508 million years ago (Cambrian period) has been identified from fossils found in Marble Canyon and Burgess Shale sites, both in British Columbia, Canada.
Dubbed Kootenayscolex barbarensis, the ancient worm was a type of annelid, a highly diverse group of animals that includes modern-day leeches and earthworms.
“While the diversity of annelids in terms of their anatomies and lifestyles makes them ecologically important and an evolutionarily interesting group to study, it also makes it difficult to piece together what the ancestral annelid may have looked like,” said Karma Nanglu, a PhD candidate at the University of Toronto and a researcher at the Royal Ontario Museum.
Although annelids are found all over the world — from the bottoms of oceans and lakes to mountain glaciers — their early evolutionary history is confounded by a poor fossil record, with few species described from well-preserved body fossils near the evolutionary origins of the group.
“While isolated pieces of annelid jaws and some mineralized tubes secreted by the animals are well known, preservation of their soft tissues is exceedingly rare,” said Dr. Jean-Bernard Caron, also from the University of Toronto and the Royal Ontario Museum.
“You need to look to truly exceptional fossil deposits like those found in the Burgess Shale to find well-preserved body fossils. Even then, they’re quite uncommon and many of the currently described species there are still poorly understood.”
Kootenayscolex barbarensis was up to 1.2 inches (3 cm) long and had hair-sized bristles on the head.
“The worm possessed paired bundles of hair-sized bristles spread along the body,” Nanglu said.
“This is one of the diagnostic features of this group of animals.”
“However, unlike any living forms, these bristles were also partially covering the head, more specifically surrounding the mouth.”
“The new 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.”
“The fine anatomical details preserved in Kootenayscolex barbarensis allow us to infer not only its evolutionary position, but also its lifestyle,” Nanglu added.
“Sediment preserved inside their guts suggests that, much as their relatives do in modern ecosystems, these worms served an important role in the food chain by recycling organic material from the sediment back to other animals that preyed on them.”
The findings are published in the January 22 edition of the journal Current Biology.
Karma Nanglu & Jean-Bernard Caron. 2018. A New Burgess Shale Polychaete and the Origin of the Annelid Head Revisited. Current Biology 28 (2): 319-326; doi: 10.1016/j.cub.2017.12.019