New Megasphaera-like microfossils reveal their reproductive strategies

Abstract

New occurrence of Ediacaran Weng’an Biota-type microfossil assemblage has been discovered from the base of the Dengying Formation in Zhenba County, Shaanxi Province, South China. The assemblage is dominated by spherical microfossils ranging from 200 to 1200μm in diameters. Based on the size and morphological features, two genera and three species have been identified, i.e. Megasphaera inornata, M. ornata and Spiralicellula bulbifera. Morphological analyses reveal three types of reproduction, i.e. binary fission, budding, and multiple fission, which are widely distributed among protist and metazoan lineages. Besides, a physiological phenomenon of “ornament growth” has been discovered among M. ornata. These again raise difficulties in determining biological affinities of Megasphaera-like microfossils. The new microfossil assemblage shares the most common elements of embryo-like microfossils with the Weng’an biota. However, those Large Acanthomorphic Acritarchs (LAAs) with great capacity for biostratigraphic correlation are not present. The age of the new assemblage is constrained within the Ediacaran, contemporary with or slightly younger than the Weng’an Biota by regional correlation. The new finding not only extends the geographical distribution of the Ediacaran phosphatized biotas in South China, but also provides valuable fossil materials for studying ontogenesis and evolution of early microscopic organisms and taphonomy of phosphatized soft-bodied fossil Lagerstätte.