Spatial Variation in the Diversity and Composition of the Early Cambrian Maotianshan Shale Biota: Taphonomic Versus Ecological Controls
Fangchen Zhao1,2†, Shixue Hu1,3, Jean-Bernard Caron4 and Maoyan Zhu1
1 Institute of Geology and Palaeontology, State Key Laboratory of Palaeobiology and Stratigraphy, Chinese Academy of Sciences, Nanjing, China
2 Chinese Academy of Sciences, Beijing, China
3 Yunnan Institute of Geological Science, Dongfeng Donglu, Kunming, China
4 Department of Palaeobiology, Royal Ontario Museum, Toronto, Ontario, Canada
Early Cambrian konservat-lagerstätten with Burgess Shale-type preservation are thought to preserve relatively unbiased records of metazoan ecosystems in the immediate aftermath of the Cambrian radiation. The degree to which species diversity and composition vary between these different ecosystems, and the factors controlling these variations, are poorly known; they have not been quantitatively explored at the level of entire fossil assemblages. The Maotianshan Shale Biota in Yunnan, China may potentially represent a good model for addressing these questions, since abundant fossils of this biota are known from many localities. In this study, we quantitatively analyzed spatial variation in species diversity and biota composition based on published diversity data for 10 localities and 19,688 specimens; and from new systematic field collections in 3 localities with comparable sedimentary features spanning 150 km. All localities are regarded as sub-contemporaneous based on the presence of the subzonal trilobite Eoredlichia-Wutingaspis.
Our study demonstrates that the diversity of the Maotianshan Shale Biota shows strong spatial variation. High diversity (210 species) characterizes the Chengjiang-Haikou-Anning areas, where the fossil-yielding strata consist of stacked couplets of thin, mm-scale single-event and background mudstone layers. Moderate diversity (55 species) characterizes the Malong-Qujing areas, where the fossil-yielding strata are composed of indistinctly bedded shale showing remnant lamination. Low diversity (26 species) characterizes the Wuding area, where the fossil-yielding strata have been intensely bioturbated. Species composition also shows spatial variation. The proportion of arthropod species varies from 33.9% to 69.9%, while priapulids range from 3.8% to 17.6%, poriferans from 0 to 18.8%, brachiopods from 0 to 9.1%, lobopods from 0 to 7.1% and hyoliths from 0 to 7.7%.
Our analyses indicate that spatial variation in the diversity and species composition of the Maotianshan Shale Biota was primarily controlled by the local geological setting, which influenced both ecological and taphonomic factors.