Newly Discovered Fossil Organism Reveals More About Evolution of Bilaterial Creatures

Scientists have uncovered a new fossil, revealing an entirely new organism from the "Ediacara Biota." The findings reveal a little bit more about the ancient Ediacaran period of geological time.

The new organism is called Plexus ricei. It resembled a curving tube and resided on the seafloor, ranging in size from 5 to 80 centimeters in length and 5 to 20 millimeters wide.  It evolved about 575 million years ago and then disappeared from the fossil record about 540 million years ago.

"Plexus was unlike any other fossil that we know from the Precambrian," said Mary Droser, one of the researchers, in a news release. "It was bilaterally symmetrical at a time when bilaterians-all animals other than corals and sponges-were just appearing on the planet. It appears to have been very long and flat, much like a tapeworm or modern flatworm."

The new fossil reveals a little bit more about this time period. Ediacaran fossils in particular don't look like any animal that is alive today, and their interrelationships are poorly understood. During the Ediacaran, no life existed on land and instead, all organisms lived in the oceans.

"Further, there was a complete lack of any bioturbation in the oceans at that time, meaning there were few marine organisms churning up marine sediments while looking for food," said Lucas Joel, one of the researchers, in a news release. "Then, starting in the Cambrian period, organisms began churning up and mixing the sediment."

This lack of bioturbation probably caused large algal mats to form on the ocean floors, and many mat-related lifestyles evolved. This, in turn, caused organisms to evolve that are far different from the ones of today. In this case, the new fossil tells scientists quite a bit about the evolution or bilaterial organisms.

"Being able to tell the difference between a tubular organism and a trace fossil has implications for the earliest origins of bilaterian organism, which are the only kinds of creatures that could have constructed a tubular trace fossil," said Joel in a news release. "Plexus is not a trace fossil. What our research shows is that the structure we see looks very much like at race fossil, but is in fact a new Ediacaran tubular organism, Plexus ricei."

The findings are published in the Journal of Paleontology.