Quantitative Paleoecology of Cambrian Burgess Shale-Type Deposits

Thanks to the exceptional preservation of diverse and abundant soft-bodied animals in rapid mud-flow (obrution) deposits, Lower to Middle Cambrian Burgess Shale-type biotas have the potential to provide key information on the composition and functioning (life habits, species interactions, and trophic relationships) of the first complex bentho-pelagic marine communities. The same deposits can also provide unique insights into short-term (i.e. ecological) and long-term (i.e. evolutionary) community patterns. Unfortunately, poor sampling, the lack of detailed analyses (faunal inventory, fine-scale sedimentology), and a traditional focus on taxonomy have limited the scope and utility of many previous quantitative paleoecological investigations at the community level.

A century after the discovery of the Burgess Shale, recent detailed quantitative paleoecological work on the Greater Phyllopod Bed (GPB-Walcott Quarry) has demonstrated that following perturbation, the Middle Cambrian community was able to recover similar sets of species across assemblages. This pattern suggests a return to a state approximating equilibrium with species richness probably controlled primarily by regional richness. Interestingly, community trends from the GPB are similar in many respects to those of modern marine benthic communities. In particular, most species in modern benthic faunas have small spatial ranges, which could be comparable with small temporal ranges of species in the GPB. Availability and characteristics of the habitat and recolonization processes were perhaps more important in structuring the community in the long-term than species interaction or short-term environmental variations at a local scale.

More studies will be necessary to evaluate differences in community patterns within and between Burgess Shale-type localities, especially to decipher the influence of paleoenvironment on the distribution of species. More generally, such knowledge could shed new light on the ecological factors that might have increased the effects of anatomical novelties during the Cambrian radiation.