Paper No. 7
Presentation Time: 9:30 AM
EARLY EVOLUTION OF MARINE TROPHIC STRUCTURES: NEOPROTEROZOIC TO CAMBRIAN
The Neoproterozoic soft-bodied Ediacaran biota was interpreted to use only two trophic mechanisms: uptake of dissolved organic material or utilization of algal symbioses. The biota was called "a peaceful garden" unlike later biotas where predation was rampant. This interpretation is flawed, and no evidence supports photoendosymbioses or the utilization of DOM. Ediacaran organisms are now recognized to include herbivores leaving scratch marks, detritovores leaving tracks, suspension feeders, and predators. Modern soft-bodied communities provide a model for the trophic roles of the ancient organisms. In these communities, animals capture and eat one another and leave no trace of it. They generally or selectively eat everything from minute to large benthos and plankton and may probe the substrata or ingest detritus. Comparisons of analogous Ediacaran organisms indicate that they too were trophically structured like these modern biotas. Predation was likely very common since the very dawn of animal life. Ediacara had herbivores, detritovores and tiered suspension feeders together with predators. It was neither peaceful nor a garden!
Cambrian trophic structures are more analogous to other Phanerozoic and modern biotas because the advent of skeletons and new body plans increased trophic strategies and complexity, in particular searching, defensive and predatory mechanisms. The Cambrian record shows mixed strategies of grazing, herbivory, predation, suspension feeding and selective and non-selective feeding on organic detritus, and photoendosymbiosis (that was more common carbonate basins of the low paleolatitudes). Evidence for these is abundant in Cambrian assemblages: infaunal and surface traces, bored and crushed shells, morphologic adaptations for feeding and photosymbioses, among others. Marine trophic structures nevertheless have been fundamentally the same, but different in aspect, since the appearance of the first large animals in the Neoproterozoic.