Pre-Cambrian microfossils discovered in rocks in southern China hint that complex multicellular life may have appeared as early as 600 million years ago.
This Megasphaera fossil displays unexpected evidence of complexity: arrow marks a matryoshka and arrowhead denotes dyads. Scale bar – 100 μm. Image credit: Lei Chen et al.
Mysterious spherical microfossils from the Ediacaran (630-542 million years ago) – the period immediately preceding the Cambrian – were uncovered from phosphorite rocks of the Doushantuo Formation in central Guizhou Province, China, in 1997.
Several previous studies have interpreted these microorganisms, called Megasphaera, as bacteria, single-cell eukaryotes, algae, bilaterally symmetrical animals or transitional forms related to modern animals such as sponges and sea anemones. However, their complete life cycle has been unknown – until now.
In a new study, published in the journal Nature, a team of paleontologists led by Dr Xunlai Yuan of the Nanjing Institute of Geology and Palaeontology describes new Megasphaera microfossils from the Doushantuo Formation that have been overlooked in the earlier studies.
These fossils represent later developmental stages of Megasphaera and show evidence for cell differentiation, germ-soma separation, and programmed cell death – qualities of complex multicellular eukaryotes such as animals and plants.
Their complex multicellularity is inconsistent with the simpler forms typically expected 600 million years ago.
“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 study co-author Prof Shuhai Xiao of the Virginia Tech College of Science.
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Lei Chen et al. Cell differentiation and germ–soma separation in Ediacaran animal embryo-like fossils. Nature, published online September 24, 2014; doi: 10.1038/nature13766
