Xunlai Yuan, a paleontologist with the Nanjing Institute of Geology and Palaeontology; Shuhai Xiao, assistant professor of geosciences at Virginia Tech; and Thomas N. Taylor, professor of ecology and evolutionary biology at the University of Kansas, report their finding in the May 13 issue of Science ("Lichen-Like Symbiosis 600 Million Years Ago").
Yuan, Xiao, and their collaborators have been exploring the Doushantuo Formation in South China for a decade and have co-authored numerous reports of fossil discoveries, including algae and animal embryos. Taylor, a member of the National Academy of Sciences, is a paleobotanist who has reported on fossil lichens in Scotland.
Lichen is a consortium of two organisms that collaborate to survive in a harsh environment, such as exposed rock. One partner, a cyanobacterium or a photosynthetic alga, or both, are able to form food from carbon dioxide, while the other partner, a fungus, provides moisture, nutrients, and protection for the consortium.
"When and where did they first learn the tricks to form this collaboration?" Xiao asked. "The earliest lichen fossils described by Professor Taylor were from non-marine deposits about 400 million years old, when plants began to massively colonize the land. But did cyanobacteria or other algae form similar relationships with fungi in the marine environment, perhaps long before the evolution of land plants?"
Present-day examples of such relationships in the sea are abundant. Now, there is an example from ancient ocean life.
At a site where abundant algae lived in a shallow sub-tidal environment about 600 m