New evidence suggests multicellularity appeared in living creatures about 60 million years before skeletal animals first appeared on the scene during a "growth spurt" of life called the Cambrian explosion.
The discovery contradicts past interpretations of the state of multicellularity 600 million years ago, Virginia Tech reported.
"This opens up a new door for us to shine some light on the timing and evolutionary steps that were taken by multicellular organisms that would eventually go on to dominate the Earth in a very visible way," said Shuhai Xiao, a professor of geobiology in the Virginia Tech College of Science. "Fossils similar to these have been interpreted as bacteria, single-cell eukaryotes, algae, and transitional forms related to modern animals such as sponges, sea anemones, or bilaterally symmetrical animals. This paper lets us put aside some of those interpretations."
The researchers looked at phosphorite rocks from the Doushantuo Formation in central Guizhou Province of South China and recovered three-dimensional fossils that showed evidence of cell-to-cell adhesion, differentiation and programmed cell death.
The findings provide insight into when solo cells started to cooperate with each other to create life forms. These new findings are inconsistent with the simple bacteria forms and single-celled life scientists believed were the only creatures in existence 600 million years ago.
Some interpretations of those ancient times may still be accurate; the idea that multicellular fossils were transitional forms related to animals or multicellular algae is still plausible. In the future the researchers hope to focus on a broader paleontological search that will map out the complete life cycle of these fossils.
"We conclude that an affinity with cellularly differentiated multicellular eukaryotes, including stem-group animals or algae, is likely but more data are needed to constrain further the exact phylogenetic affinity of the Doushantuo fossils," the researchers stated in their study abstract.
The findings were made in collaboration with the Chinese Academy of Sciences and were published in the Sept. 24 journal Nature.
