COORDINATED STASIS - BIOFACIES REVISITED AND THE CONCEPTUAL MODELING OF WHOLE-FAUNA DYNAMICS

The observation of stratigraphic intervals characterized by faunas dis playing ''coordinated stasis'' in the Appalachian Basin of New York St ate (Brett and Baird, 1995) is based on the existence of biofacies. Th us, any claims as to the significance or unusual nature of patterns of coordinated stasis are really statements about these underlying biofa cies common features of the fossil record that have long been recogniz ed. Evaluation of the bimodal distribution of evolutionary and ecologi cal change through time apparent in biofacies and Ecological Evolution ary subunits must be done in relation to the clearly stated expectatio ns of null models. The evolutionary and ecological bases for such mode ls are explored here using a conceptual approach founded on two ecolog ical and two evolutionary neutral ''rules'': (1) communities are capab le 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 thi s conceptual framework are discussed. Documentation of environmental d ynamics, alongside faunal dynamics, seems to be the key to understandi ng whether biofacies and coordinated stasis fall outside our expectati ons.