Data from: Diversity of cnidarians and cycloneuralians in the Fortunian (early Cambrian) Kuanchuanpu Formation at Zhangjiagou, South China

The latest discovery of microfossils from lower Cambrian (Fortunian Stage) Zhangjiagou Lagerstätte in South China are presented. This lagerstätte is rich in exceptionally preserved microfossils, including embryos of Olivooides multisulcatus, Olivooides mirabilis, and Pseudooides prima, hatched stages of O. multisulcatus, O. mirabilis, Hexaconularia sichuanensis and Quadrapyrgites quadratacris, and cycloneuralians represented by Eopriapulites sphinx and a new form. The largest known fragment of O. mirabilis implies that its adults length can be more than 9.0 mm with at least 50 annuli, and the longest known specimen of Q. quadratacris has at least 18 annuli. These unusually large specimens refute the non-feeding larvae hypothesis for Olivooides and Quadrapyrgites. New material documented here includes two new types of fossil embryos, one with hexaradial symmetry and the other with octaradial symmetry, as well as a new cycloneuralian with two tail spines. Based on the current material, it is inferred that 1) early cnidarians have a high diversity in the Fortunian Stage; 2) P. prima might represent the embryonic stages of H. sichuanensis; 3) adults of Olivooides and Quadrapyrgites may have reached centimeter scale dimensions with more than 50 annuli; 4) Olivooides and Quadrapyrgites may be better interpreted as coronate scyphozoans; 5) cycloneuralians also had a high diversity in the Zhangjiagou Lagerstätte; and 6) cycloneuralians might have originally been part of the early Cambrian meiofauna rather than belonging to the macrobenthos. Such ancestral cycloneuralians might have been Eopriapulites-like, possessing pentaradially symmetric, backward pointing, and internally hollow introvert scalids used as locomotory devices.

本研究报道了产自中国南方下寒武统幸运阶（Fortunian Stage）张家沟特异埋藏化石库（Lagerstätte）的最新微体化石发现。该特异埋藏化石库保存有大量精美的微体化石，涵盖多槽橄榄形虫（Olivooides multisulcatus）、奇异橄榄形虫（Olivooides mirabilis）以及初级假形虫（Pseudooides prima）的胚胎化石，多槽橄榄形虫、奇异橄榄形虫、四川六锥虫（Hexaconularia sichuanensis）与方形四锥虫（Quadrapyrgites quadratacris）的孵化后幼体阶段化石，以及以狮始曳形虫（Eopriapulites sphinx）和一新类型为代表的环神经动物类群（cycloneuralians）化石。目前已知最大的奇异橄榄形虫化石碎片表明，其成体体长可超过9.0毫米，且至少具有50个体环；而已知最长的方形四锥虫标本则至少拥有18个体环。这些体型异常硕大的标本，推翻了橄榄形虫属与四锥虫属营非摄食幼虫阶段的假说。本次研究记述的新材料包含两类全新的胚胎化石：其一为六辐射对称类型，其二为八辐射对称类型；同时还发现了一具带有两枚尾棘的全新环神经动物类群化石。基于当前的化石材料，可得出以下六点推论：1）幸运阶时期的早期刺胞动物（cnidarians）具有极高的类群多样性；2）初级假形虫可能是四川六锥虫的胚胎发育阶段；3）橄榄形虫属与四锥虫属的成体体长或可达厘米级，且体环数量超过50个；4）橄榄形虫属与四锥虫属或许更应被归类为冠群钵水母类（coronate scyphozoans）；5）张家沟特异埋藏化石库中的环神经动物类群同样具有较高的类群多样性；6）环神经动物类群最初或许属于早寒武世小型底栖生物（meiofauna），而非大型底栖生物（macrobenthos）。这类原始的环神经动物类群可能与始曳形虫属物种形态相近，拥有用于运动的五辐射对称、向后指向且内部中空的翻吻棘（introvert scalids）。