Bryozoans (also known as ectoprocts or moss animals) are aquatic, dominantly sessile, filter-feeding lophophorates that construct an organic or calcareous modular colonial (clonal) exoskeleton^1,2,3. The presence of six major orders of bryozoans with advanced polymorphisms in lower Ordovician rocks strongly suggests a Cambrian origin for the largest and most diverse lophophorate phylum^2,4,5,6,7,8. However, a lack of convincing bryozoan fossils from the Cambrian period has hampered resolution of the true origins and character assembly of the earliest members of the group. Here we interpret the millimetric, erect, bilaminate, secondarily phosphatized fossil Protomelission gatehousei⁹ from the early Cambrian of Australia and South China as a potential stem-group bryozoan. The monomorphic zooid capsules, modular construction, organic composition and simple linear budding growth geometry represent a mixture of organic Gymnolaemata and biomineralized Stenolaemata character traits, with phylogenetic analyses identifying P. gatehousei as a stem-group bryozoan. This aligns the origin of phylum Bryozoa with all other skeletonized phyla in Cambrian Age 3, pushing back its first occurrence by approximately 35 million years. It also reconciles the fossil record with molecular clock estimations of an early Cambrian origination and subsequent Ordovician radiation of Bryozoa following the acquisition of a carbonate skeleton^10,11,12,13.

苔藓虫（也称为 ectoprocts 或苔藓动物）是水生的、主要无柄的、以滤食性为食的有鳞动物，可构建有机或钙质的模块化殖民地（克隆）外骨骼^1,2,3。在下奥陶纪岩石中存在六种具有高级多态性的主要苔藓虫目，强烈表明最大和最多样化的二、四、五、六、七、八的寒武纪^起源。然而，缺乏令人信服的寒武纪苔藓虫化石阻碍了对该群体最早成员的真实起源和特征组合的解析。在这里，我们解释了毫米、直立、双层、二次磷酸化的化石Protomelission gatehousei ⁹来自澳大利亚和华南的早寒武世作为潜在的茎群苔藓虫。单形动物蒴果、模块化结构、有机组成和简单的线性萌芽生长几何形状代表了有机裸毛虫和生物矿化的 Stenolaemata 特征性状的混合物，系统发育分析将 P.gatehousei 鉴定为茎群苔藓虫。这将苔藓虫门的起源与寒武纪 3 世纪的所有其他骨架化门对齐，将其首次出现推迟了大约 3500 万年。它还将化石记录与早期寒武纪起源的分子钟估计和随后获得碳酸盐骨架^10,11,12,13后苔藓虫的奥陶纪辐射相协调。