508 million years ago, a strange worm was scratching at the Earth’s seabed: it had no eyes, it had two tentacles that sprouted from its head and it was covered with bristles, so much so that it would have resembled a scrub brush that you can find in any kitchen.
The exquisitely preserved fossil remains of this strange creature, named Kootenayscolex barbarensis , have been discovered in Canada; and the authors of the finding have published their curious description in the journal Current Biology .
What is so extraordinary about this new creature?
Like other worms that also have bristles, Kootenayscolex barbarensis has them in the form of a kind of hair that protrudes from its body. “However, unlike any other life form, these bristles also partially covered the head, more specifically, around the mouth, ” according to a statement from the Department of Ecology and Evolutionary Biology at the University of Toronto and a researcher at the Museum. Royal Ontario.
The marine worm is one of the first complex animals on the face of the Earth, originated during an era known as the Cambrian Explosion : the first appearance of the most modern groups of animals in the fossil record.
The answer to an evolutionary mystery
By analyzing the fossils, the researchers are closer to solving an evolutionary mystery about how ringed worms, a group that includes modern day worms and leeches, developed their heads.
In the case of this new creature, it appears that the head of the annelid evolved from posterior body segments that had pairs of bristles, a hypothesis supported by the developmental biology of many modern species of annelids.
The bristling worm was small, just 2.5 centimeters long. But this small body possessed about 1,400 bristles : each of the 25 body segments carried 56 bristles, and it also had two long tentacles on its head. Also, smaller antennae present between its tentacles would likely help the worm to dig into the ground.
The discovery of the Kootenayscolex barbarensis is not the first to be made at Marble Canyon, an archaeological site located within the Burgess Shale deposit. Between 2012 and 2016, scientists have discovered more than 500 worm fossils, also corresponding to the stage of the Cambrian Explosion.
It probably fed on muddy deposits on the seabed. “These organisms funnel mud into their mouths and then sift for organic material to feed on,” according to Dr. Karma Nanglu, one of the authors of the research, who has obtained this evidence from the well-preserved intestine of the Kootenayscolex.
“The design and composition of these elements help us formulate hypotheses about what type of tissues the animal originally possessed,” explains Nanglu.
Image: Royal Ontario Museum.
References: ‘A New Burgess Shale Polychaete and the Origin of the Annelid Head Revisited. Karma Nanglu, Jean-Bernard. Current Biology (2018). Doi: http://dx.doi.org/10.1016/j.cub.2017.12.019.
