Foote 9506568 This research will (1) use explicit data on skeletal anatomy to document evolutionary radiations in Paleozoic and Mesozoic crinoids, and (2) test for a proposed difference between evolutionary radiations at different taxonomic scales by comparing the radiation of crinoids as a whole to the radiations of the constituent subgroups of crinoids. Evolutionary radiations, involving substantial increases in the number of named taxa and in morphological diversity, are among the most prominent features of the fossil record. It is commonly thought that evolutionary radiations at different taxonomic, temporal, and spatial scales do not differ significantly in temporal patterns or underlying mechanisms. This perspective has scarcely been tested directly. There are some hints that there may be a major difference between the evolutionary radiations of higher taxa (clades) and the lower taxa (subclades) nested within them, namely that morphological diversification within subclades is more gradual in time than diversification of the larger clade to which they belong. However, these suggestions have been based on case studies that are not ideally suited to test this idea. By comparing the Paleozoic radiation of a major invertebrate group, the Crinoidea, to that of subsidiary crinoid clads that diversified concurrently with the larger crinoid clade, I will test for the existence of such a discordance between taxonomic ranks. The Mesozoic radiation of articulate crinoids will provide an additional comparison. The results will help to answer questions about the hierarchical nature of evolution and our ability to predict larger-scale evolutionary patterns from smaller-scale patterns. Changes in morphological diversity, or disparity, during evolutionary radiations are usually assessed by using proxies such as the number of higher taxa (mainly classes and orders). There are a number of reasons to question the adequacy of such proxies. The proposed research will use direct quantification o f morphology to study evolutionary radiations in crinoids. I will use discrete morphological characters to quantify crinoid form, and will measure morphological disparity based on the net dissimilarities among species. I will apply a number of quantitative approaches, including "clade-shape" statistics, to explore the temporal pattern of morphological expectations of various evolutionary models. The proposed research will answer questions about the generation of morphological diversity over long spans of evolutionary time, and will develop a morphological database that can be used by other workers to investigate a wide range of issues, including phylogenetic relationships, evolutionary rates, and trends.
