Are Nemiana Palij and Beltanelliformis Menner (Beltanelloides (Sokolov)) synonyms or different genera?

Abstract

During recent decades, the issue of the nature of Ediacaran cyclic imprints, including the widely distributed in Podillia (southwestern Ukraine) Nemiana simplex Palij, 1976, and the less common Beltanelliformis brunsae Menner, 1974 (Beltanelloides sorichevae (Sokolov), 1965) has been actively debated. Several new and similar forms were discovered in other regions of the Globe. The disk-like outlines were considered to be sufficient characters to synonymize several earlier recognized genera and species. The main additional features used to distinguish cyclic genera included such features as the shape and sculpture of surfaces, facial differences, and geological age. Novel palaeobiochemical studies of these ancient remains opened a new phase of discussions on the possible identities of the organisms that formed these fossil structures. Sometimes the remains are covered with thin brown films providing biochemical evidence for the cyanobacterial nature of some structures, for example Beltanelliformis brunsae. However, these films are found only in clayey or carbonate environments (rocks). For Nemiana Palij, characteristic features are clustered communities and budding. In contrast, Beltanelliformis brunsae formed taphonomic communities of closely arranged disks almost identical in their shape and size. Nemiana simplex structures are confined to clastic rocks (mostly thin-grained sandstones or siltstone), which are not suitable for good preservation of imprints and organic remains of ancient animals, cyanobacteria, algae, and plants. Considering these and some additional considerations, synonimization of Nemiana та Beltanelliformis, as well as some other Ediacaran fossil structures differing in their morphology, is at best premature.