The Burgess Shale paleocommunity with new insights from Marble Canyon, British Columbia

The middle (Wuliuan Stage) Cambrian Burgess Shale is famous for its exceptional preservation of diverse and abundant soft-bodied animals through the "thick" Stephen Formation. However, with the exception of the Walcott Quarry (Fossil Ridge) and the stratigraphically older Tulip Beds (Mount Stephen) which are both in Yoho National Park (British Columbia), quantitative assessments of the Burgess Shale have remained limited. Here we first provide a detailed quantitative overview of the diversity and structure of the Marble Canyon Burgess Shale locality based on 16,438 specimens. Located 40 km southeast of the Walcott Quarry in Kootenay National Park (British Columbia), Marble Canyon represents the youngest site of the "thick" Stephen Formation. We then combine paleoecological datasets from Marble Canyon, Walcott Quarry, Tulip Beds and for the first time, the Raymond Quarry, which lies ca. 20 m directly above the Walcott Quarry, to yield a combined species abundance dataset of 77,179 specimens encompassing 234 taxa. Material from the Tulip Beds comes from talus slopes whereas material from all the other localities was collected in situ and comes from stratigraphically constrained intervals of at least 2 m. Marble Canyon shows significant temporal changes in both taxonomic and ecological groups, suggesting periods of stasis followed by rapid turnover patterns at local and short temporal scales. At wider geographic and temporal scales, the different Burgess Shale sites occupy distinct areas in multivariate space. Overall, this suggests that the Burgess Shale palaeocommunity is far patchier than previously thought and varies at both local and regional scales through the "thick" Stephen Formation. This underscores that our understanding of Cambrian diversity and ecological networks, particularly in early animal ecosystems, remains limited and highly dependent on new discoveries.

寒武纪武里安阶（Wuliuan Stage）的布尔吉斯页岩（Burgess Shale）以其在‘厚层’斯蒂芬组（Stephen Formation）中保存了多样且丰富的软躯体动物而闻名于世。然而，除了均位于不列颠哥伦比亚省（British Columbia）约霍国家公园（Yoho National Park）的沃尔科特采石场（Walcott Quarry，化石岭Fossil Ridge）与地层年代更早的郁金香床（Tulip Beds，产于斯蒂芬山（Mount Stephen））外，针对布尔吉斯页岩的定量研究仍十分有限。本研究首先基于16438件标本，对大理石峡谷（Marble Canyon）布尔吉斯页岩产地的生物多样性与群落结构展开详细的定量概述。该产地位于不列颠哥伦比亚省库特尼国家公园（Kootenay National Park）内沃尔科特采石场东南40公里处，是‘厚层’斯蒂芬组已知最年轻的化石产出点。随后，本研究整合了来自大理石峡谷、沃尔科特采石场、郁金香床以及首次纳入的雷蒙德采石场（Raymond Quarry，位于沃尔科特采石场正上方约20米处）的古生态数据集（paleoecological datasets），最终构建得到包含234个分类群（taxa）、总计77179件标本的合并物种丰度数据集。郁金香床的化石样品采自塌积坡（talus slopes），而其余所有产地的样品均为原位（in situ）采集，且采自至少2米厚的地层限定层位。大理石峡谷产地的分类群与生态类群均呈现出显著的时间变化，指示局地短时间尺度下存在停滞期后快速更替的群落动态模式。在更大的地理与时间尺度上，不同布尔吉斯页岩产地在多元空间（multivariate space）中占据截然不同的区域。整体而言，这表明布尔吉斯页岩古群落（palaeocommunity）的斑块化程度远高于此前认知，且在‘厚层’斯蒂芬组的沉积过程中，其群落结构在局地与区域尺度上均存在变化。这进一步凸显出，我们对寒武纪生物多样性与生态网络（ecological networks），尤其是早期动物生态系统的认知仍十分有限，且高度依赖新的化石发现。