2026-014-21 中国科学院（CAS）
Cambrian Fortunian annelids. A–C, Kuanchuanpivermis brevicruris, holotype; B–D, Zhangjiagoivermis longicruris, holotype. (Image by ZHANG Huaqiao)
＜関連情報＞
- https://english.cas.cn/newsroom/research-news/202604/t20260420_1157585.shtml
- https://www.pnas.org/doi/10.1073/pnas.2538071123
カンブリア紀初期の多毛類環形動物 Polychaete annelids from the earliest Cambrian Period
Xiaofeng Xian, Huaqiao Zhang, Shuhai Xiao, +2 , and Baichuan Duan
Proceedings of the National Academy of Sciences Published:April 20, 2026
DOI:https://doi.org/10.1073/pnas.2538071123
Significance
Annelids (ringed worms) possess an epidermis which secretes a collagenous cuticle prone to decay. Therefore, they have relatively low fossilization potential and have left very few articulated body fossils. Previously reported annelid body fossils in the Cambrian Period come exclusively from Burgess Shale-type fossil localities (<521 Myr old), with compressed two-dimensional preservation. In this study, we report three-dimensionally preserved body fossils of annelids from an early Fortunian Orsten-type fossil locality (ca. 535 Myr old). These represent the oldest known body fossils of annelids in the Phanerozoic and suggest that the earliest Cambrian annelids may have differentiated into polychaete morphologies and that annelids may have had an evolutionary history prior to the Cambrian explosion.
Abstract
Unambiguous body fossils of annelids (ringed worms) first appear in the Cambrian Period but are so far known exclusively as flattened specimens preserved in Burgess Shale-type Lagerstätten. Here, we report phosphatized microfossils, interpreted as polychaete annelids, from a distinct taphonomic window (i.e., three-dimensional Orsten-type preservation) in the earliest Cambrian (early Fortunian Age, ca. 535 Ma) Zhangjiagou Lagerstätte of South China. The fossils are millimetric in length and preserved as three-dimensional endocasts of the body. They exhibit clear trunk segmentation, with each segment bearing a pair of lateral or ventrolateral outgrowths. Two species, Kuanchuanpivermis brevicruris gen. et sp. nov. and Zhangjiagoivermis longicruris gen. et sp. nov., are distinguished based on the relative length of these outgrowths. The lateral outgrowths terminate in a bifurcation into two lobes of equal, subequal, or unequal size, closely resembling the notopodium and neuropodium of annelid parapodia. Both species are interpreted as members of the total-group Annelida. Kuanchuanpivermis brevicruris has relatively short appendages and may have been a benthic annelid similar to modern nereids. Zhangjiagoivermis longicruris closely resembles fossil and extant polychaetes (e.g., Eotomopteris and Tomopteris) in their relatively long appendages, suggesting a swimming lifestyle and representing the earliest known semi-pelagic annelid. These findings indicate that annelids had already acquired a polychaete-like body plan in the Fortunian and that early members of the clade had diverged from their living sister group and differentiated into forms with both short and elongate parapodia by the Fortunian Age.
