Two ribbon-like macrofossils in contrasting preservational styles from the Ediacaran–Cambrian interval

The fossil record of the latest Ediacaran and earliest Cambrian comprises diverse tubular and ribbon-like macrofossils of uncertain affinities, some of which could record early metazoans and macroalgae. This study compares two ribbon-like macrofossils typical of Ediacaran–Cambrian intervals, investigating their morphology, potential affinities, and biostratigraphic significance: Rugosusivitta, preserved as essentially two-dimensional carbonaceous compressions, and Harlaniella, preserved as casts and molds. It is shown that the recently described Rugosusivitta orthogonia Tang et al., 2021 resembles the tube-like Harlaniella ingriana in its morphology, characterized by a combination of transverse ridges and longitudinal stripes separated into distinct parts of an elongate body. This combination of features challenges algal or protistan affinities, leaving open the possibility of metazoan origins. Both Rugosusivitta and Harlaniella likely represent body fossils rather than ichnofossils consistent with their preservation as either carbonaceous compressions or sediment-infilled tubes, respectively. By reconstructing the global distribution of Rugosusivitta and Harlaniella in different taphonomic windows, we suggest that these fossils record a coherent morphotype spanning the Ediacaran–Cambrian boundary.