Statistical tests of coordinated stasis within the Middle Devonian Hamilton Group demonstrate significant temporal changes in taxonomic composition and ecological structure of the macrofauna throughout a 5–6 m.y. time span. The analysis, based upon a collection of >38,000 specimens obtained over a 20 yr period from the Hamilton Group of central New York, used highly controlled sampling techniques, applied within a single, well-defined lithofacies. Assemblages were tested for stability through time, as would be predicted by the model of coordinated stasis. Our results reveal that within at least one major Hamilton environment, taxonomic and ecological stability are not statistically significant and therefore do not support the hypothesis of coordinated stasis.