The fossilised remnants of tube-like ‘dwellings’ which housed a primitive type of prehistoric sea worm on the ocean floor have been identified in a new study. According to researchers, the long, perforated tubes may have looked like narrow chimneys reaching up from the sea bed, and were made by a creature called Oesia, which lived a solitary existence inside them about 500 million years ago.
The study suggests that in some cases these structures exceeded 50cm in height and that they were typically at least twice the width of the worm, giving it plenty of room. The ends were sealed off, making life inside a rather lonely experience. “Only single worms are found within tubes, suggesting a solitary mode of life,” Nanglu added.
At some point, the fossil record suggests that acorn worms underwent a transition, leaving their tubes and instead opting for a life under the sea bed. The study argues that as evolution gathered pace and more predators appeared on the scene, digging into the sea floor may simply have been a safer option. Certainly, modern-day acorn worms have adopted this lifestyle; rather than filter feeding they live in the sediment and eat nutrients within it.
“In its own depressing way this is a story of Darwinian competition,” Conway Morris explained. “The levels of competition and predation increased, life sped up and got harder, and animals had to protect themselves more. One way of doing this was to abandon life filter feeding in a tube, and instead to dig into the sediment and eat mud. Once there, they found a new niche and were able to make a perfectly good life for themselves.” Paper. (public access) – Karma Nanglu, Jean-Bernard Caron, Simon Conway Morris, Christopher B. Cameron. Cambrian suspension-feeding tubicolous hemichordates. BMC Biology, 2016; 14 (1) DOI: 10.1186/s12915-016-0271-4 More.
Conway Morris is engaging in classic Darwinian storytelling. We don’t know why the worms moved from the tubes to under the seabed. Changing water environment was eating the tubes? There is nothing the matter in principle with his speculation about competition but too often these days, Darwinian storytelling stands in for actual knowledge. And people do not notice the difference.
The problem is that, after a while, stories build on stories and a body of false information can build up.
See also: Stasis: Life goes on but evolution does not happen