EVALUATING MODERN AND FOSSIL DIVERSITY IN THE COMATULID CRINOIDS

The purpose of this study is to explore the bias resulting from taxonomic practice in the comatulid crinoids. The comatulids show an order of magnitude increase in generic diversity between the modern and most recent fossil time bin. This increase in measured diversity is described as real change + error + bias. There are many potential sources of bias, but a prominent one is differing taxonomic practice. Neontologic descriptions of comatulids generally focus on arm traits, while paleontologic descriptions have focused on the discrete and easily recognized centrodorsal element. This means that a modern species may not be the taxonomic equivalent of a fossil species. Assessing these effects will bring us closer to understanding the real change as well as focus on removing the effects of other biases, including rock record volume, paleontologic research effort, and collection effort.

By artificially degrading the modern record, this study removes a potential source of bias in comparisons of modern and fossil diversities of comatulid crinoids. By focusing only on the centrodorsals, modern comatulid morphotypes can be directly compared to fossil morphotypes. This can consequently serve as a guide for removing other biases from the diversity curve. For example, if there is a large difference between fossil and modern diversity within a geographic region that may indicate that further paleontologic efforts should be undertaken in appropriate strata. Further work will use the morphological and ecologic variation of the centrodorsal in modern comatulids to make inferences about ecology and morphospace occupation in the past.