NEW VIEWS OF OLD ALGAE: VORONOCLADUS (CHLOROPHYTA) FROM THE SILURIAN OF UKRAINE AND A MAJOR EARLY PALEOZOIC MACROALGAL RADIATION

Voronocladus dryganti Skompski et al., 2023 was recently erected as a new genus and species of noncalcified dasycladalean alga on the basis of material from the Ludlovian Konivka Formation of western Ukraine. The monopodial thalli, as carefully described in that report, are remarkable not only for their exceptional preservation, mainly as carbonaceous compressions, but also for showing unusual structures at the top, which were interpreted as epibionts. Here, an alternative interpretation is proposed for this material. In it, the affinity of Voronocladus as a siphonous green macroalga is retained, but as a bryopsidalean rather than dasycladalean alga, and the graptolite-like structures at the top are considered to represent the uppermost siphons of mature thalli instead of epibionts. Viewed in broader terms, the reinterpreted morphology of Voronocladus is important because it (1) adds to a wide array of complex thallus morphologies rapidly evolved by siphonous green macroalgae during and shortly after the GOBE, a key factor in the replacement of the preceding Cambrian Flora by the Ordovician Flora, and (2) helps to resolve the outlines of a major radiation of bryopsidalean algae during this timeframe. The latter event, which is only now beginning to come into focus and includes the evolution of Caulerpa- and Codium-like forms, coincides with a major radiation of dasycladalean algae and, collectively, these radiations could be viewed as signaling something akin to a biotic revolution, the trigger for which was elevated marine herbivory and the outcomes of which affected other components of the Earth System.