ABUNDANCE-BASED PALEOECOLOGY OF THE EARLY CAMBRIAN MAOTIANSHAN SHALE BIOTA: ECOLOGIC DOMINANCE OF PRIAPULID WORMS

The Early Cambrian soft-bodied Maotianshan Shale biota of Yunnan Province, China provides a critical glimpse of animal life during the heart of the Cambrian radiation.  It contains at least three distinctive fossil assemblages: the Chengjiang, Haikou, and Shankou biotas.  This research is part of a long-term 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 Shankou biota is the focus of current work, and 9,963 specimens from it have been examined and tallied thus far.  Only specimens thought to be buried alive, based on either soft-part preservation or fully articulated complex skeletons, were counted.  Algae were too numerous to count.  Initial results reveal that the three most abundant genera comprise 43.2% of all specimens: the tube-dwelling priapulid worm Paraselkirkia (16.0%), the diminutive priapulid worm Protopriapulites (14.3%), and the brachiopod Heliomedusa (12.9%).  No other genera total more than 9% of specimens.  Two of these three dominant genera, Paraselkirkia and Heliomedusa, were adapted to firm substrates.  The abundance of genera adapted to firm substrate conditions is consistent with previous paleoecological studies based on generic diversity.  At the phylum level, there is an interesting dichotomy between taxonomic diversity and ecologic dominance.  The arthropods are the most taxonomically diverse phylum in the Shankou biota, comprising 21 of 57 genera (37%).  The priapulids, however, are easily the most abundant phylum, comprising 43.2% of all specimens in the biota.  Arthropods (26.3%) and brachiopods (19.6%) are the second and third most abundant phyla respectively.  All other phyla together comprise only 10.9% of the biota.  Because of their sheer abundance, this study indicates that priapulid worms exerted more influence on energy flow and community structure than other phyla in this particular trophic web.  This result contrasts strongly with traditional views of Maotianshan Shale biota paleoecology, which often claimed arthropod dominance based solely on taxonomic diversity.