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.

寒武纪武都统（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享誉学界。然而，除了均坐落于不列颠哥伦比亚省优鹤国家公园（Yoho National Park）内的沃尔科特采石场（Walcott Quarry，化石岭（Fossil Ridge）），以及地层年代更早的郁金香床（Tulip Beds，斯蒂芬山（Mount Stephen））之外，针对布尔吉斯页岩的定量研究始终较为有限。本研究首先基于16438件化石标本，对库特尼国家公园（Kootenay National Park，不列颠哥伦比亚省）内、沃尔科特采石场东南40千米处的大理石峡谷（Marble Canyon）布尔吉斯页岩产地的物种多样性与群落结构展开详细的定量概览。该产地是“厚层”斯蒂芬组已知最年轻的化石位点。随后，我们整合了来自大理石峡谷、沃尔科特采石场、郁金香床，以及首次纳入分析的、距沃尔科特采石场正上方约20米的雷蒙德采石场（Raymond Quarry）的古生态数据集，最终得到包含234个分类群（taxa）、总计77179件标本的合并物种丰度数据集。郁金香床的化石材料采自岩屑坡，而其余所有产地的化石标本均为原地（in situ）采集，且来自地层限定的至少2米厚的沉积层位。大理石峡谷的分类群与生态类群均呈现出显著的时间演替特征，表明在局部尺度与短时间跨度内存在停滞期后快速更替的群落变化模式。在更大的地理与时间尺度下，不同布尔吉斯页岩化石位点在多元空间中占据着截然不同的分布区域。总体而言，这表明布尔吉斯页岩古群落（palaeocommunity）的空间斑块性远高于此前的认知，且在“厚层”斯蒂芬组的沉积过程中，其群落结构在局部与区域尺度上均存在显著变化。这凸显出我们对寒武纪生物多样性与生态网络，尤其是早期动物生态系统的认知仍较为有限，且高度依赖新的化石发现。