ECOLOGICAL DOMINANCE OF THE PRIAPULID WORM CRICOCOSMIA IN A MAOTIANSHAN SHALE BIOTA COMMUNITY

The early Cambrian soft-bodied Maotianshan Shale biota of Yunnan Province, China provides a crucial view of animal life during the heart of the Cambrian radiation. It contains a minimum of three distinctive fossil assemblages: the Chengjiang, Haikou, and Shankou biotas. This research is part of a project to provide a comprehensive understanding of the paleoecology of each of these biotas through abundance-based studies of collections housed at the Early Life Research Center in Chengjiang. No specimens were discarded during excavation of these biotas, ensuring that each of them represents a time-averaged paleocommunity. The Haikou biota is the focus of this study, and 7,621 specimens from it have been examined and tallied. Only specimens interpreted as having been buried alive, based on the presence of either undecayed soft-part preservation or fully articulated complex skeletons, were counted. Initial results reveal that the three most abundant genera comprise 62.4% of all specimens: the priapulid worm Cricocosmia (33.2%), the arthropod Leanchoilia (17.4%), and the diminutive priapulid worm Protopriapulites (11.8%). No other genera total more than 7% of specimens. Previous abundance-based studies of the Haikou biota indicated arthropod dominance (Hu, 2005). These contrasting results are attributable to differing methodologies. Whereas Hu (2005) counted all specimens, including disarticulated skeletal elements, the method utilized in this study attempted to count a census of animals living at the time of burial. There is a decoupling of taxonomic diversity and ecological dominance at the phylum level in the Haikou biota. Arthropods are the most taxonomically diverse phylum, comprising 23 of 54 genera (43%). The priapulids, on the other hand, are the most abundant phylum, comprising 55.9% of all specimens in the biota. Arthropods (30.6%) are the second most abundant phylum. All other phyla together comprise only 13.5% of the biota. Because of their relative abundance, this study indicates that priapulid worms were competitive dominants in this community, exerting the most influence on energy flow, community structure, and species composition. This result also indicates that animal evolution during the Cambrian radiation occurred largely in the context of priapulid ecological dominance.