Sponges may be ancient, but their timeline has been murky. New research suggests the earliest sponges were soft and skeleton-free, explaining why their fossils don’t appear until much later. By analyzing hundreds of genes and modeling how skeletons evolved, scientists found that mineralized spicules arose separately in different sponge lineages. The discovery rewrites the story of how the first reef-building animals—and possibly the first animals of all—emerged.
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