THE EFFECT OF VARIABLE GEOGRAPHIC COVERAGE ON ESTIMATIONS OF ORIGINATION AND EXTINCTION: A CASE STUDY ON THE HAMILTON GROUP OF NEW YORK

It is well demonstrated that variation in sampling intensity and coverage can greatly modify our understanding of standing biodiversity, origination, and extinction through time. As the sampled area increases, a wider variety of habitats is likely to be sampled. As other authors have noted, if an environment or group of environments is missing from the sampled record, last appearances will peak, and first appearances of taxa with a preference for that habitat will be delayed until that habitat is next sampled. If organisms change their geographic ranges to reflect changes in their environment, this could have a profound effect on our estimates of rates of turnover. Coincidental movement of taxa would exacerbate this effect. Faunas of the Hamilton Group of New York have long been noted for their taxonomic stability despite changes in their geographic ranges associated with fluctuations in the geometry of the Appalachian basin. Here we assess the impact of changing ranges and variable coverage on estimations of rates of origination and extinction. To do this we are constructing a database of fossil occurrences for New York State. To date, the subset of our database focusing on the Hamilton Group consists of roughly 6000 generic occurrences from approximately 300 collections. Over the next year we hope to increase our sampling intensity for the Hamilton Group. and expand our temporal coverage from the Ordovician to the latest Devonian, with an end goal of intensive coverage from the New York –Pennsylvania border and from the Hudson River to Lake Erie. Known occurrences of taxa are combined with geographic and stratigraphic data. Origination and extinction rates can then be calculated for a range of geographic subsets of the dataset, allowing us to determine how temporal variation in geographic ranges affects our understanding of turnover rates.