Exceptionally preserved fossils from China reveal that bryozoans had been already thriving in the course of the Cambrian explosion.
More than half a billion years in the past, the Cambrian explosion reshaped life on Earth, giving rise to almost each main animal lineage alive as we speak. Yet regardless of greater than a century of fossil discoveries, one group remained conspicuously absent. Bryozoans, tiny colonial animals that carpet fashionable reefs and seafloors, appeared to look tens of hundreds of thousands of years too late, leaving scientists with one of the final main unanswered questions on this pivotal interval in evolution.
Now, exceptionally preserved fossils from southern China have stuffed that hole. Dating to about 520 million years in the past, the fossils present that bryozoans had been already thriving in the course of the Cambrian explosion, overturning the concept that they developed a lot later and offering some of the strongest proof but that almost all main animal teams emerged throughout this exceptional evolutionary radiation.
The fossils are extraordinary not solely as a result of of their age but additionally as a result of of their preservation. They retain microscopic anatomical options that permit researchers to confidently establish the animals as bryozoans, resolving a decades-long debate over their identification and pushing the group’s evolutionary origins even deeper into Earth’s previous.
The Evolutionary Enigma Solved
Reporting in Nature, scientists from China, Sweden, Australia, and Germany describe exceptionally preserved fossils from the Xiannüdong Formation in southern Shaanxi Province, China. The materials consists of new examples of the beforehand identified Protomelission gatehousei and a newly recognized taxon, Dayingomelission hexaclitia gen. et sp. nov. Both date to the early Cambrian, about 520 million years in the past.
“Bryozoa has been the elephant in the room of Cambrian paleontology for a long time,” stated co-author Dr Timothy Topper of Northwest University and the Swedish Museum of Natural History. “Every other major animal phylum had a Cambrian representative, except bryozoans. These fossils, finally, close that chapter for good.”
The fossils are vital not solely as a result of of their age, but additionally as a result of of how a lot element they protect. The tiny colonies, just a few millimeters throughout, had been fossilized in three dimensions, with inner gentle tissues nonetheless preserved and mineralized by phosphate.
With superior imaging strategies, the researchers recognized tremendous anatomical options, together with membranous sacs, structural spines referred to as types, and even particular person muscle fibers. They additionally discovered the distinctive hexagonal, modular association of zooid skeletons that characterizes bryozoan colonies. Taken collectively, the skeletons and gentle tissue anatomy strongly help their identification as bryozoans.
“These specimens are remarkable; to have soft tissues mineralized inside their original skeletal housing, half a billion years later, is nothing short of extraordinary,” stated Professor Zhifei Zhang of Northwest University, the research’s corresponding creator. “These bryozoans lived in shallow, clear-water reef environments, which may explain why they have eluded discovery for so long; the Cambrian fossil sites best known for soft-tissue preservation invariably represent deeper-water settings.”
Rewriting the timeline
The fossils do greater than fill a lacking chapter within the fossil report. They additionally change how scientists perceive the bryozoan household tree. A phylogenetic evaluation locations each Cambrian taxa throughout the crown group Stenolaemata, one of the three predominant courses of residing bryozoans. Because these fossils already sit on a complicated department of the group, bryozoans should have originated even earlier, probably way back to the Ediacaran interval earlier than the Cambrian explosion started.
The new proof additionally challenges earlier claims that P. gatehousei may not be a bryozoan. Some researchers had proposed that it could possibly be a inexperienced alga or remoted sclerites from one other sort of organism. The newly preserved gentle tissues, together with detailed comparisons of colony measurement, form and inner construction, rule out these different explanations and supply a transparent hyperlink to bryozoans.
“These aren’t just simple precursors; they are complex, modular colonies,” explains Baopeng Song, the research’s lead creator. “The combination of skeletal architecture and internal anatomy provides definitive evidence that these are true bryozoans, and that the phylum was already diversifying during the Cambrian radiation.”
Together, the 2 Chinese taxa and beforehand reported Cambrian fossils from South Australia point out that bryozoans had been extra widespread in early Cambrian oceans than beforehand acknowledged. They additionally present that these animals had been already extremely developed. Their colonial physique plan, by which genetically similar people referred to as polypides work collectively inside a shared skeleton, now seems to have been a central innovation of the Cambrian explosion reasonably than a later evolutionary arrival.
Reference: “High-fidelity modular skeletons authenticate a Cambrian origin for Bryozoa” by Baopeng Song (宋宝鹏), Zhifei Zhang (张志飞), Luke C. Strotz, Timothy P. Topper, Andrej Ernst, Junye Ma (马俊业), Zhiliang Zhang (张志亮), Mei Luo (罗梅), Lars E. Holmer, Yue Liang (梁悦), Yazhou Hu (胡亚洲), Caibin Zhang (张彩彬), Yanlong Chen (陈延龙) and Glenn A. Brock, 3 June 2026, Nature.
DOI: 10.1038/s41586-026-10590-9
This research was financially supported by the National Key Research and Development Program of China (grant 2023YFF0803601 to Zhifei Zhang), the National Natural Science Foundation of China (grantW2441016 to L.C.S.), the Department of Science and Technology of Shaanxi Province (2022TD-11 to Zhifei Zhang) and 111 Project (D17103).
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