寒武纪大爆发时期, 以动物为主导的海洋生态系统已初步构建完成。腕足动物作为这一时期海生底栖群落的重要代表, 建立了复杂的多层次生态分层(Tiering)结构。华南寒武纪一些特异埋藏化石群中出现大量单属种腕足动物壳体富集保存的现象, 对当时海洋底质的硬化改造以及生态系统的复杂化发挥了重要意义。黔东剑河革东地区苗板坡、金银山和承多三个剖面的凯里生物群(寒武纪乌溜期)中普遍产出腕足动物化石密集层, 其中以舌形贝型亚门(Linguliformea)的伯瑞堂古圆货贝(Palaeobolus bretonensis)占据绝对主导地位。此外, 密集层中还有较多的古盘虫类三叶虫、少量蠕形动物、软体动物和始海百合等底栖生物共同保存。研究显示, 凯里生物群中腕足动物密集层内的化石保存较好, 几乎全部平行于层面保存, 壳体大小不一, 无明显定向性, 判断为生物成因的原地埋藏群落。化石层面和岩石光面显示, 除了微弱的水平层理, 密集层未见其他强水动力的沉积构造和生物扰动痕迹, 指示凯里生物群中以腕足动物为主导的生物群落可能在安静的水体环境中被沉积事件原地掩埋, 未遭受流体侵蚀或搬运作用。通过建立生态结构理论模型和对比分析, 显示凯里生物群中腕足动物主导的古群落在物种多样性和生态空间利用率方面都要高于滇东寒武纪第四期的关山生物群。同时, P. bretonensis壳体上固着有始海百合动物, 可能反映密集层中复杂的底栖群落关系, 表明寒武纪乌溜期大量繁盛的带壳腕足动物为泥质软基底上的底栖生物提供了更多生态空间。

The Cambrian Explosion represents the mysterious radiation of disparate bilaterian animals and the first emergence of marine ecosystems dominated by the animal kingdom. Brachiopods are one of the most important contributors to the tiering complexity through the Palaeozoic. The lower Cambrian strata of South China yield such a wide variety of monospecific or paucispecific brachiopod shell concentrations. Here we present the first record of a brachiopod-dominated community from the Kaili Biota (Wuliuan, Miaolingian) at the Chengduo, Jinyinshan and Miaobanpo sections in Jianhe County, Guizhou Province, South China. The association occurs on the same bedding plane that is dominated by linguloid brachiopod Palaeobolus bretonensis, commonly alongside pelagic pagetiids, infaunal worms, epibenthic molluscs, and eocrinoids. The shells of P. bretonensis on the bedding plane, both juveniles and adults, appear to be randomly orientated. Nearly all individuals of P. bretonensis are disarticulated, but shells with fine concentric sculptures are common and concordant to the bedding plane. Polished sections perpendicular to the bedding plane show that the layer containing the brachiopod shell concentrations lacks other sedimentary structures and bioturbations, indicating a quiet, low energy environment. Taphonomic and sedimentological evidences demonstrate that the shell pavements herein are basically biogenic and preserved in situ. Ecological structural models for the brachiopod-supported communities from the Kaili and the Guanshan biotas are partly overlapping. However, the Kaili Biota shows a higher biodiversity and more complexity in ecological tiering or feeding strategies. The shell pavements of P. bretonensis from the Kaili Biota probably had an effect in hardening the soft substrates and provided more possible niches for other benthos such as the eocrinoids during the middle Cambrian.

国家自然科学基金(41890845, 42162003, 42202005)、贵州省人才基地项目(RCJD2018-21)、贵州省科技计划(黔科合平台人才2017-5788)和江苏省自然科学基金青年基金(BK20221151)联合资助