Characterization of the Multicellular Membrane‐Bearing Algae From the Kuanchuanpu Biota (Cambrian: Terreneuvian)

• Published in: Journal of geophysical research. Biogeosciences 2021-06, Vol.126 (6), p.n/a
• Main Authors: Zheng, Yajuan, Tang, Qingqin, Liu, Ping, Sun, Jie, Yao, Xiaoyong, Hao, Wenjing, Yang, Xiaoguang, Guo, Junfeng, Uesugi, Kentaro, Komiya, Tsuyoshi, Han, Jian
• Format: Article
• Language: English
• Subjects: agglomerate fossils; Aggregates; Algae; Animal embryos; Biota; Cambrian; Cell differentiation; Cell size; Cell walls; Clumps; Cyanobacteria; Cytology; Differentiation (biology); Embryos; Encapsulation; Food sources; Fossils; Life cycle; Life cycles; Marine ecosystems; Membranes; Morphology; multicellular algae; Physical characteristics; Synchrotrons; Tomography
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2020JG006102

The diversity of small shelly fossils (SSFs) demonstrates that multicellular organisms underwent large‐scale radiation at the beginning of the Cambrian, which is highlighted by the coexistence of various metazoans and the occurrence of their embryo fossils. However, little is known about early Cambrian eukaryotic multicellular algae, the primary producers that replaced oxygenic cyanobacteria and played a crucial ecological role in matter cycling and energy dynamics in marine ecosystems. In this study, hundreds of microscopic three‐dimensionally preserved multicellular aggregate fossils were obtained from the Kuanchuanpu Formation (Cambrian: Terreneuvian, ca. 535 Ma) in southern Shaanxi, South China, which consisted of several tightly packed multicellular clumps encapsulated in a thin organic membrane. Synchrotron tomography analysis further revealed that the cells of the whole aggregate, although partitioned into different clumps by a gelatinous membrane, were distinctly differentiated into an outer conical cell layer and an inner spherical‐cell layer, thus suggesting of a cortex‐medulla‐like differentiation. These characteristics resemble those of multicellular algae (e.g., Wengania, Gremiphyca, and Thallophyca) from the Weng'an biota (Ediacaran, South China) in morphology, size, and internal cell structure. Furthermore, a potential asexual life cycle for these membranous algae was proposed based on their morphological and structural characteristics. Plain Language Summary Hundreds of microscopic three‐dimensionally preserved multicellular aggregate fossils were obtained from the early Cambrian Kuanchuanpu Formation (ca. 535 Ma) in southern Shaanxi, South China, which consisted of several tightly packed multicellular clumps encapsulated in a thin organic membrane. Based on the basic morphology, external membranes, spatial configuration, cell differentiation, and particularly the presence of a cell wall, it is more reasonable to interpret the Kuanchuanpu aggregate fossils as the multicellular algae, rather than cyanobacteria or metazoan embryos. The size, morphology, and cortex‐medulla differentiation pattern of these aggregate fossils consist with the characteristics of multicellular algae from the Weng'an biota (Ediacaran, China). The discovery of aggregate algae in the Kuanchuanpu biota may provide critical insights for a better understanding of the evolution and fate of the multicellular algae during the Ediacaran–Cambrian transition period. The aggreg