SciTechDaily has an interesting story about some of the earliest sponges. New research in the journal Nature suggests the earliest sponges did not have a mineral skeleton. Virginia Tech geobiologist Shuhai Xiao and his collaborators described a Ediacaran (550 million years old) sponge that had not evolved the ability to generate the hard needle-like structures, known as spicules, that characterize sea sponges today.
Xiao’s team members traced sponge evolution through the fossil record. As they went further back in time, sponge spicules were increasingly more organic in composition and less mineralized.
“If you extrapolate back, then perhaps the first ones were soft-bodied creatures with entirely organic skeletons and no minerals at all,” Xiao said. “If this was true, they wouldn’t survive fossilization except under very special circumstances where rapid fossilization outcompeted degradation.”
Later in 2019, Xiao’s international research group found a sponge fossil preserved in just such a circumstance: a thin bed of marine carbonate rocks known to preserve abundant soft-bodied animals, including some of the earliest mobile animals.
