Morphological reconstruction of the Ediacaran macroalga Gesinella from South China

Abstract

Macroalga Gesinella, a carbonaceous compression, is found in the upper part of Doushantuo Formation (Ediacaran) in the Yangtze Platform of South China. Morphologically, it is composed of a thallus (including an oval or oblong lamina and a short-rod-like stipe) and a holdfast (including a cone-shaped rhizome and many filamentous rhizoids). The cone-shaped rhizome connects with the stipe and the long rhizoids grew on the rhizome, meaning that the rhizome grew downwards and inserted into the sediment, while the rhizoids grew in the gaps between the sediment grains to anchor its body on the seafloor. On the lamina, branching and/or unbranching filaments are regularly distributed, so that the oval or oblong lamina can be interpreted as a sac-like body that has been compressed. The filaments on the lamina extend from the three-dimensionally preserved stipe, suggesting that the short-rod-like stipe may have been flexible to support the sac-like body in the water column. With tissue and organ differentiations, Gesinella can be regarded as a eukaryotic macroalga and a high-level metaphyte. Based on measurement and analysis of 108 specimens, the Ediacaran macroalga Gesinella from South China can be divided into three stages: juvenile stage (<3 mm maximum width) identified with difficulty, adult stage (3–10 mm maximum width) interpreted to have grown upwards for sunlight, and senescent stage (>10 mm maximum width) that grew sideways.