Scientists say they have discovered the earliest known example of an animal evolving to lose body parts it no longer needed.
Facivermis, a worm-like creature that lived approximately 518 million years ago in the Cambrian period, had a long body and five pairs of spiny arms near its head, leading to suggestions it might be a “missing link” between legless cycloneuralian worms and a group of fossil animals called lobopodians, which had paired limbs all along their bodies.
But a new study by the University of Exeter and the Natural History Museum in the UK and China’s Yunnan University reveals Facivermis was itself a lobopodian that lived a tube-dwelling lifestyle anchored on the sea floor, and so evolved to lose its lower limbs.
Lead author Richard Howard says it is the earliest known example of “secondary loss”, which is seen today in cases such as the loss of legs in snakes.
“A key piece of evidence was a fossil in which the lower portion of a Facivermis was surrounded by a tube,” he says. “We don’t know the nature of the tube itself, but it shows the lower portion of the worm was anchored inside by a swollen rear end.
“Living like this, its lower limbs would not have been useful, and over time the species ceased to have them.”
The findings are published in the journal Current Biology.
Originally published by Cosmos as If lower limbs aren’t used, get rid of them
Cosmos
Curated content from the editorial staff at Cosmos Magazine.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today.
