Utilizing Phylogenetic and Geochemical Techniques to Examine Echinoderms Through Time

Understanding biotic changes through Earth’s history has been the goal of paleobiology since the inception of the field. Advances in science and technology have progressed allowing us to reassess old questions and new questions that could have not been addressed without these new methods. Echinoderms (sea stars, sea urchins, etc.) appear in the fossil record during the early Cambrian and are still abundant in marine ecosystems today. This persistence through time has made echinoderms model organisms to answer questions about Earth’s past and present. Despite this role as a model organism there are many questions that remain with respect to evolutionary history and biogeochemistry of echinoderms. The research herein therefore focuses on a combination of phylogenetics and geochemistry.

First, I explore the phylogenetics of Paracrinoidea. Paracrinoidea is a clade of Paleozoic echinoderms that exhibit unusual morphologies. These morphologies have hindered our understanding of their phylogenetic relationships and character evolution. This study represents the first rigorous, quantitative phylogenetic analysis of Paracrinoidea. Both a phylogenetic hypothesis and phylomorphospace were generated to inform patterns seen in morphology with an evolutionary perspective.

To explore echinoderm geochemistry, I examined major and minor element inclusion in echinoderm skeletal elements from four genera of modern echinoids from the Gulf of Mexico. These echinoids show measurable variation in skeletal composition which indicates a complex relationship between skeletal element growth rate and geochemical composition. These results help inform the utility of fossil echinoderms in geochemical studies and highlights the need for continued study of elemental incorporation in echinoderm skeletal elements.

Finally, I explore the geochemistry of fossil echinoderms. Fossilization and diagenetic processes can alter the original chemistry of the fossilized skeletal elements and impact their utility as seawater proxies. This study used both petrographic and geochemical techniques to assess the retention of original chemistry of fossil echinoid skeletal elements. Results highlight the need for caution and petrographic work to determine the retention of original chemistry to assess the utility of echinoderms as proxies. This work highlights the utility of echinoderms as case study organisms and the power of combined analyses to elucidate biotic changes during the Phanerozoic.