They believe the fossil, dubbed the Bicellum Brasieri, shows an organism that is between a single cell and multicellular animal.
The fossil reveals new insight into the transition of single-celled organisms to complex multicellular animals, according to scientists.
Its discovery has been described in a new research paper published in Current biology.
Professor Charles Wellman is one of the lead investigators of the research from the University of Sheffield’s Department of Animal and Plant Sciences.
He said: “The origins of complex multicellularity and the origin of animals are considered two of the most important events in the history of life on Earth, our discovery sheds new light on both of these.
“We have found a primitive spherical organism made up of an arrangement of two distinct cell types, the first step towards a complex multicellular structure, something which has never been described before in the fossil record.
“The discovery of this new fossil suggests to us that the evolution of multicellular animals had occurred at least one billion years ago and that early events prior to the evolution of animals may have occurred in freshwater like lakes rather than the ocean,” he added.
Its “exceptional preservation” allowed the scientists to analyse it at a cellular and subcellular level.
The team now hopes to examine the deposits for more interesting fossils which could provide further insight into the evolution of multicellular organisms.
Professor Paul Strother, lead investigator of the research from Boston College, said: “Biologists have speculated that the origin of animals included the incorporation and repurposing of prior genes that had evolved earlier in unicellular organisms.
