COMPARATIVE COMMUNITY PALEOECOLOGY OF THE EARLY CAMBRIAN (SERIES 2, STAGE 3) CHENGJIANG BIOTA FROM CHINA

Lagerstätten from the Precambrian-Cambrian transition have traditionally been a relatively untapped resource for understanding paleoecology of the Cambrian Explosion. Systematic collections of fossil assemblages from narrow stratigraphic intervals of the Chengjiang and several other lagerstätten that provide abundance as well as presence-absence information are now available for comparative analysis. At the Mafang (near Haikou, Kunming City, Yunnan Province) section, where one of the richest Chengjiang fossil deposits exists, fossil specimens were systematically collected from a single quarry covering 58.3 m² through 2.5 m thickness. The fossiliferous deposit consists of stacked couplets of millimeter to centimeter thick event mudstone layers (rapid deposition) and background mudstone layers (slow deposition). The 2.5m thickness of the sampled section was subdivided into several mutually contiguous sampling intervals. Only specimens from event mudstones interpreted as buried alive, based on either soft-part preservation or fully articulated skeletons, were counted. A total of 10,238 fossil specimens from 10 fossil assemblages were analyzed, belonging to 100 species representing 11 phyla and 15 ecological categories. The results reveal a single community with stable taxonomic membership overall that is dominated by epibenthic vagile hunters or scavengers, sessile suspension feeders, and infaunal vagile hunters or scavengers represented primarily by arthropods, brachiopods and priapulids respectively. Comparisons with similar paleoecological samples from the Burgess Shale suggest that the overall structure and ecology of Cambrian communities remained relatively stable until at least the Middle Cambrian in subtidal siliciclastic soft substrate environments. Comparison can also be made with similar data from the Ediacara Biota (Mistaken Point), and modern shallow marine benthic communities. Although there are significant ecological differences between these communities and those of the Cambrian, the data indicates a similar range of values with an increasing trend through time, which supports the view that communities trended towards more complexity, diversity and stability within broad-scale ecological processes since marine benthic macroscopic organisms first evolved.