Pre-Phanerozoic carbonaceous megafossils are generally considered to be the remains of metaphytic algae. While these fossils are not particularly common, they are significant for the understanding on the global evolutionary level of the pre-Phanerozoic biota. Ribbon-shaped vendotaenids were interpreted as brown algae and represent the youngest, most common and geographically most widespread Precambrian carbonaceous megafossils. It now appears that they may be better understood as abandoned giant sheaths of sulfide oxidizing organotrophic bacteria related to the Modern Thioptoca among the Beggiatoaceae. □Thallophyta, algae, methaphytes, Vendotaenidae, late Proterozoic, Precambrian, Vendian, bacteria.