Development of the trophic structure of Vendian and Early Paleozoic marine communities

Major trophic links are reconstructed for the Vendian and Early Paleozoic. A hypothesis of the predominant development of extracorporeal or skin digestion in Vendian multicellular consumers is substantiated. The main food sources were algal-bacterial films, finely dispersed debris falling from the photic zone in cold shallow seas lacking a thermocline and debris on the surface of the sediment. Symbiosis with phototrophic and chemotrophic bacteria was widespread. Pelagic filtration and filtration of the near-bottom finely dispersed organic matter (including bacteria), and debris-feeding appeared when internal digestion became widespread in the Cambrian. These were supplemented in the Ordovician by feeding on the live phyto- and zooplankton in the water column one meter above the bottom. Before the Ordovician, feeding on live plankton and more so active predation on larger multicellular animals was the exception rather than the rule. The role of active predators in the biota did not become more important until the end of the Silurian. Mass morphogenesis among occurred multicellular animals as the amount and diversity of nutritional and/or spatial resources rapidly increased, while before that the lack of these was a limiting factor.