Bryozoans, small colonial animals, were traditionally believed to have appeared millions of years after the Cambrian explosion. However, remarkable fossils discovered in 520 million-year-old rocks in China reveal that these fascinating creatures have been present since the dawn of time.
Reconstruction of the early Cambrian ocean floor showing Protomerision Gatehouse and Daingomellission Hexacritia flourishing in the shallow waters of Archaeossias Reef. Image credit: Zhifei Zhang.
“Bryozoans are small, filter-feeding, colonial invertebrates that continue to thrive in the world’s oceans today. Yet, their origins remained a mystery for decades,” noted paleontologist Dr. Timothy Topper from Northwest University and the Swedish Museum of Natural History.
“While nearly all other major animal groups emerged during the Cambrian explosion around 530 million years ago, the fossil record for bryozoans remained conspicuously absent until the Ordovician period, roughly 50 million years later.”
In a groundbreaking study, paleontologists analyzed a stunning bryozoan fossil from the early Cambrian Sennudo Formation in China.
The samples represent two species: Protomerision Gatehouse and a newly recognized taxon, Daingomellission Hexacritia.
“For too long, bryozoans have been the missing link in Cambrian paleontology,” Dr. Topper stated.
“Except for bryozoans, all other significant animal phyla have Cambrian representations. This discovery definitively closes that gap.”
Specimen of Protomerision Gatehouse excavated from the sacrolactoid layer where a membranous sac is preserved. Image credit: Song et al., doi: 10.1038/s41586-026-10590-9.
This discovery not only fills a significant gap in the fossil record but also has profound implications for our understanding of the tree of life.
Phylogenetic analysis firmly places both Protomerision Gatehouse and Daingomellission Hexacritia within the Crown Group Stenolaemata, one of the three main classes of living bryozoans.
Since these fossils represent a more advanced branch of the Bryonidae family tree, their existence suggests that the origin of the entire group might date back to the Ediacaran period, even before the Cambrian explosion.
This study also confirms that Protomerision Gatehouse is indeed a bryozoan, despite some researchers proposing it might be a sclerotid derived from green algae or another unrelated organism.
New soft tissue data, along with detailed comparisons of colony size, shape, and internal structure, refute these alternative interpretations, clearly solidifying their association with bryozoans.
Specimen of Daingomellission Hexacritia showcasing colonies and cystids from the Xiannüdong Formation. Image credit: Song et al., doi: 10.1038/s41586-026-10590-9.
“These are not merely precursors; they are complex, modular colonies,” asserts paleontologist Baopeng Song from Northwest University.
“The combination of skeletal structure and internal anatomy provides definitive evidence that these represent true bryozoans, indicating that this phylum was already diversifying during the Cambrian radiation.”
“Together, the two Chinese taxa and previously reported Cambrian material from South Australia suggest that bryozoans were not only widespread in the early Cambrian oceans but also highly sophisticated in their development.”
“The concept of colonial body planning, where genetically identical individuals known as polypids cooperate within a communal skeleton, appears to have evolved as a core innovation of the Cambrian explosion itself rather than a late development.”
The team’s paper is published in the latest edition of Nature.
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B. Song et al. The high-fidelity modular skeleton proves the Cambrian origin of bryozoans. Nature, published online on June 3, 2026. doi: 10.1038/s41586-026-10590-9
Source: www.sci.news
