At Discovery (December 7, 2011), Jennifer Viegas tells us, “Earth’s earliest animals may have looked just like baseballs”:
Previous theories have said that the fossils represented giant bacteria.
“One of the proponents of the bacteria theory was a co-author of this paper (Jake Bailey of the University of Minnesota) and he now agrees that the fossils do not represent a giant sulfur bacteria,” co-author Philip Donoghue, a professor of palaeobiology at the University of Bristol, told Discovery News.
With the bacteria hypothesis negated, that leaves a few possibilities as to what these unusual fossils represent. One, argued by Xiao and others, is that the fossils are of metazoan embryos. If so, they would present one of the oldest records of the animal evolutionary lineage.
We’ll keep the file open. Some say they are protists.