A new study finds that these controversial fossils are not likely to be bacteria or single-celled protists; their cells, preserved for more than 600 million years in rock, are too complex and differentiated. Instead, the fossils may be multicellular algae, or even the embryosof ancient animals.
“The real value of these fossils is that we now have some direct evidence about how this transition from single-celled organisms to things like animals and plants occurred in the evolutionary past,” said study researcher Shuhai Xiao, a geobiologist at Virginia Tech in Blacksburg.
The bizarre fossils, known as Megasphaera, come from a rock layer in southern China called the Doushantuo Formation. Xiao first studied Megasphaera specimens in 1998 and suspected that they might be animal embryos.
Each fossil measures a mere 0.03 inches (0.7 millimeters) or so across and comes from what would have been a shallow marine environment at the time.
But no adult animals that might have produced these embryos have ever been found, leaving the identity of the fossils open to scrutiny. Previous Megasphaera fossils studied have been extracted from a gray rock in the Doushantuo Formation, Xiao told Live Science. Now, he and his team have succeeded in extracting more difficult-to-see fossils from the formation’s black rocks.