THE IMPORTANCE OF BIOTIC INTERACTIONS IN SHAPING EDIACARAN BENTHIC COMMUNITIES: A COMPARATIVE CASE STUDY OF THE GAOJIASHAN AND MISTAKEN POINT BIOTAS

During the last 10 million years of the Ediacaran Period (551–541 Ma), the marine realm witnessed an extensive faunal transition from communities of large, enigmatic, mostly sessile, “classic Ediacarans” to vermiform dominated communities, known from such localities as the Nama Group, Gaojiashan Lagerstätte, and Deep Spring Formation. This new ecosystem presented a variety of novel ecological strategies, including biomineralization and reef-building, that may have been elicited by increased pressures from inter- and intra-specific competition and presumably newly evolved macropredation. Through the application of quantitative and survivorship analyses to body size estimates of the two most populous vermiform taxa from the Gaojiashan Lagerstätte in South China, we have constructed a more complete picture of how these early animals may have responded to competition, with a focus on space availability and reproductive/recruitment success. We propose a model whereby the larger, flat-lying, possibly mobile taxon, Gaojiashania, outcompeted the formerly dominant upright growing, Conotubus, by means of increased space occupation, leading to the decrease of substrate space necessary for successful recruitment (settling and attachment) of Conotubus. Furthermore, we applied corresponding analyses to body size estimates of classic Ediacaran taxa from the Mistaken Point assemblage in Newfoundland from the previously published data of Clapham et al. (2003), a collection of in situ fossils that has been cited as possible evidence for early competition in the form of epifaunal tiering. Comparative analysis of the Gaojiashan taxa with their enigmatic predecessors present two very different responses to fluctuations in diversity and abundance of co-occurring taxa, begging the question as to when we truly see our first evidence of ecologically antagonistic competition.