The Kuanchuanpu biota (ca. 535 Ma) from the basal Cambrian in South China yields various phosphatized, three-dimensionally preserved microscopic fossils, such as animal embryos, cyanobacteria, and algae. This provides an exceptional window for investigating the rapid divergent evolution of animal phyla in the early Cambrian ocean. However, the fossil eukaryotic algae are poorly documented and are not properly incorporated into the conceptual food web of the Cambrian ocean ecosystem. In this study, we report a new taxon of calathiform alga, Calathophycus irregulatus Tang gen. et sp. nov., and an indeterminate alga, from the Kuanchuanpu biota. Calathophycus irregulatus can be distinguished from other reported phosphatized multicellular algal fossils from the Kuanchuanpu biota and the Ediacaran Weng’an biota (Guizhou Province, China), based on the external morphology and features of cell clump aggregation. The observation of C. irregulatus and the indeterminate alga indicates a certain diversity of algae at the beginning of the Cambrian. Concerning the regularly or irregularly shaped multicellular algal fossils from the Kuanchuanpu Formation, co-occurring spherical fossils, previously interpreted as “cleavage stage” of animal embryos, should be reconsidered in affinity.

Key words: Algal fossils, bowl-shaped fossils, early Cambrian, Kuanchuanpu biota.

Qing-Qin Tang [tangqingqin@stumail.nwu.edu.cn], Xiao-guang Yang [lqzy0301@gmail.com], Jie Sun [shuibaobei@ vip.qq.com], and Jian Han [elihanj@nwu.edu.cn], Shaanxi Key Laboratory of Early Life and Environments (SKLELE), State Key Laboratory of Continental Dynamics (SKLCD), Department of Geology, Northwest University, Xi’an 710069, China. Ya-Juan Zheng [yajuanzheng@126.com], School of Earth Science and Resources, Key Laboratory of Western China’s Mineral Resources and Geological Engineering, Ministry of Education, Chang’an University, Xi’an 710054, China. Song Qin [sqin@yic.ac.cn] and Yin-Chu Wang [ycwang@yic.ac.cn], Yantai Institute of Coastal Zone Research, Chinese Academy of Science, Yantai, 264003, China. Xing Wang [wx5432813@126.com], Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China. Kentaro Uesugi [ueken@spring8.or.jp], Japan Synchrotron Radiation Research Institute (JASRI), Hyogo, Japan. Tsuyoshi Komiya [komiya@ea.c.u-tokyo.ac.jp], Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan.