The fossil creature in question represents the earliest evidence that an animal with limbs ends up losing limbs, in the course of evolution, through lack of use.
The worm-like creature, called Facivermis , lived about 518 million years ago during the Cambrian period , a time in history when there was a rapid diversification of complex, multicellular life forms.
Facivermis lived underwater: its body was long and thin and had five pairs of spiny arms, suggesting it could be a "missing link" between legless cycloneural worms and a group of fossil animals called lobopodia. However, he lost his lower limbs over time due to disuse. He lost his legs to engage in a better lifestyle inhabiting the tubes.
One more step in the tree of life.
Reference: Richard J. Howard et al. A Tube-Dwelling Early Cambrian Lobopodian. Current Biology, published online February 27, 2020; doi: 10.1016 / j.cub.2020.01.075
