Quantitative paleoecology of marine faunas in the lower Hamilton Group (Middle Devonian, central New York): Significance for probing models of long-term community stability

Abstract

Beautifully fossiliferous strata in the Hamilton Group (Middle Devonian, central New York) constitute a rich "ecological archive" sufficient to probe and test foundational concepts in paleontology. The evident community stability of Hamilton faunas over 4-6 m.y.-including two proposed mechanisms for coordinated stasis-has ignited controversy. Resolving community structure and both taxonomic and ecological temporal persistence within the Hamilton Group thus becomes critical to testing whether these Hamilton communities are stable and whether they are ecologically "locked." Toward this end, we conducted multivariate analyses (cluster and correspondence analysis) of marine faunas in 81 large samples (~300 specimens each) in shallowing-upward sequences of the Cardiff and Pecksport Members (Marcellus Subgroup, Oatka Creek Formation) of the Hamilton Group. Eight statistically and ecologically distinctive benthic communities characterize the vertical gradient, from depauperate, deeper-water dark shales below to species-rich shelf siltstones above. These communities correlate strongly with grain size, bioturbation intensity, bedding thickness, density of fossils, and faunal and ecological diversity. Species richness varies inversely with weight percent organic matter. We characterized taxonomic distributions using multivariate statistics; these statistical analyses were based on percentages of 50 taxa. In order of decreasing depth, the communities are: Cephalopod-Pterochaenia, Pterochaenia-Eumetabolotoechia, Eumetabolotoechia, Emanuella, Eumetabolotoechia-Ambocoelia, Arcuaminetes-Eumetabolotoechia, Arcuaminetes-Ambocoelia, and Mucrospirifer-Ambocoelia. The Cephalopod-Pterochaenia community represents a mixed benthicpelagic fauna associated with the deepest and finest-grained facies. The Pterochaenia-Eumetabolotoechia, Eumetabolotoechia, and Emanuella communities have low to