The helically coiled microfossil Obruchevella from the upper Ediacaran Miaohe Member in South China

Abstract

Exceptionally preserved fossils from Precambrian strata are crucial for our understanding of the origin and evolution of early life on Earth. Some of them (e.g., Obruchevella) are comparable with extant forms in cellular morphology, indicating remarkable evolutionary conservatism or morphological convergence. Here we describe abundant and exceptionally preserved specimens of Obruchevella from the upper Ediacaran Miaohe Member in South China. The new specimens are characterized with a helical filament, a diagnostic feature of the genus Obruchevella, but many of them also have an elongate, axially arranged, rod structure. The axial rod is probably a taphonomic artifact, although we also consider its possible biological origin. Should the axial rod be proven as biological in origin, it may represent a previously undocumented component of Obruchevella, or an organism distinct from but symbiotically associated with Obruchevella. These uncertainties highlight the challenges in distinguishing taphonomic and biological structures in Precambrian microfossils despite their exceptional preservation. Regardless, the new microfossils provide new taphonomic and morphological insights into Obruchevella, which is considered as a morphological analog of the modern cyanobacteria Spirulina and Arthrospira. They also enrich the microfossil diversity of the Miaohe Member, which is better known for macroscopic carbonaceous compression fossils.