Tiny fossils have solved a decades-old mystery about early animal life, shedding light on the evolution of bryozoans, tiny filter-feeding animals that build colonies of near-identical individuals sharing one skeleton. These creatures, which coat rocks, shells, and seaweed across the world’s oceans, have long been a subject of debate due to their apparent absence from the fossil record during the Cambrian explosion, a period when most major animal body plans emerged. The discovery of two distinct colony forms in China, dating back 520 million years, has revealed that bryozoans were not only present but already branching into different kinds, challenging previous assumptions. The preservation of soft tissue, including muscle fibers and sac-like internal linings, in these fossils, has provided crucial evidence that they are indeed animals, not seaweed or loose plates from unrelated creatures. This finding places the origin of bryozoans firmly within the Cambrian explosion, indicating that their colonial lifestyle was an early innovation in animal evolution. The study, published in the journal Nature, not only settles a long-standing debate but also opens up new avenues for paleontological research, suggesting that shallow Cambrian reefs worldwide may hold more significant fossil deposits than previously thought.
