Coordinated stasis: biofacies revisited and the conceptual modeling of whole-fauna dynamics

The observation of stratigraphic intervals characterized by faunas displaying “coordinated stasis” in the Appalachian Basin of New York State (Brett and Baird, 1995) is based on the existence of biofacies. Thus, any claims as to the significance or unusual nature of patterns of coordinated stasis are really statements about these underlying biofacies — common features of the fossil record that have long been recognized. Evaluation of the bimodal distribution of evolutionary and ecological change through time apparent in biofacies and Ecological Evolutionary subunits must be done in relation to the clearly stated expectations of null models. The evolutionary and ecological bases for such models are explored here using a conceptual approach founded on two ecological and two evolutionary neutral “rules”: (1) communities are capable of considerable compositional flux, (2) multiple stable states are available to communities, (3) allopatry is the main mode of speciation, and (4) stabilizing selection is effective. The aspects of biofacies that appear counter-intuitive when compared to the predictions of this conceptual framework are discussed. Documentation of environmental dynamics, alongside faunal dynamics, seems to be the key to understanding whether biofacies and coordinated stasis fall outside our expectations.