Independent origins of spicules reconcile paleontological and molecular evidence of sponge evolutionary history

Abstract

Sponges (Porifera) are ecosystem engineers that play a critical role in global biogeochemical processes. Their evolution is key to understanding Neoproterozoic paleoecology but remains mired in controversy. Molecular timescales suggest a Tonian or Cryogenian origin, while their oldest unequivocal fossils consist of disarticulated siliceous spicules from the Late Ediacaran. We derived a new, dated sponge phylogeny and tested whether ancestral sponges had mineralized skeletons. We resolve the sponge phylogeny in good agreement with current knowledge and date their origin to the early Ediacaran. Our results suggest that early sponges were not biomineralized and that both biosilicification and biocalcification evolved independently multiple times across Porifera. We reconcile fossil evidence and molecular estimates of sponge evolution by showing that the Neoproterozoic history of Porifera is limited to the Ediacaran and providing evidence suggesting that sponges are largely absent from the Ediacaran record because they were yet to evolve biomineralized skeletons.