Bizarre Worm-like Creature Lost Its Legs 518 Million Years Ago Because They Were No Longer Useful

An alien-like species of lobopodian is the primary recognized instance of evolutionary reversion. Scientists writing in Current Biology defined the creature discarded its again limbs for a less complicated, and sometimes extra primitive, physique form.

Facivermis was a worm-like species with an extended, skinny form and 5 spiny arms on the highest a part of its physique. Its backside half was limbless, melding right into a swollen backside that helped anchor the animal to the seafloor. The species inhabited the planet roughly 518 million years in the past, through the Cambrian interval, when it might filter particles of meals within the water.

The creature has mystified scientists since its discovery 30 years in the past. Some professionals have recommended it was a “missing link” creature bridging the hole between legless cycloneuralian worms and lobopodians, that are worm-like creatures with pairs of limbs sandwiching its physique. Only now do scientists know the place this bizarre-looking creature suits into the evolutionary tree because of well-preserved fossils collected from the Chengjiang Biota in Yunnan Province, southwest China.

Analysis of those fossils places facivermis firmly within the Cambrian lobopodian group—one which preceded three trendy animal teams, together with Arthropoda (i.e. together with bugs, shrimps and spiders), Tardigrada (i.e. water bears) and Onychophora (i.e. velvet worms).

Facivermis illustration
An illustration of a facivermis, the primary species recognized to have misplaced its limbs.
Franz Anthony

Crucially, facivermis show the earliest recognized instance of a phenomenon referred to as “secondary loss,” whereby it misplaced its legs in a similar way to modern-day snakes. A examine not too long ago revealed in Science Advances described as species of historic snake that existed with hind limbs for some 70 million years. As Newsweek reported on the time, it was seemingly simply one among many who went by means of such a change.

The type of evolution is antithetical to what we anticipate. In most situations, organisms evolve to have extra complicated physique constructions—not less complicated.

“Occasionally we see the opposite occurring,” senior writer Xiaoya Ma mentioned in an announcement. “What excited us in this study is that even at this early stage of animal evolution, secondary-loss modifications— and in this case, reverting ‘back’ to lose some of its legs—had already occurred.”

Lead writer Richard Howard defined that an vital clue to its improvement was a selected fossil the place the creature’s decrease half was encased in a tube.

“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,” he mentioned in an announcement. “Living like this, its lower limbs would not have been useful, and over time the species ceased to have them.”

It seems to be distinctive amongst its relations, who tended to have someplace between three and 9 pairs of decrease legs made for strolling. In distinction, facivermis could have been caught in a single place.

Illustration of Facivermis
The standing of the facivermis has puzzled scientists for hundreds of years.
Franz Anthony

Leave a Comment