Date of Award

5-2017

Document Type

Thesis

Department

Environmental and Forest Biology

Thesis Advisor

Rebecca J. Rundell

Abstract

Despite their vast diversity, few metazoan lineages have made the transition from marine to terrestrial habitats. These transitions must have been accompanied by dramatic shifts in the physiology and ecology of the lineages, marking major evolutionary events that have shaped the diversity we see today. Among the Metazoa, gastropod molluscs have been among the most successful at making the transition, comprising at least 12 separate transitions. This unusual history makes them particularly suitable for studying the evolutionary context of these major events. The development of new relaxed molecular clock methods for seamlessly integrating molecular and fossil data provides new possibilities for determining the timing of evolutionary events. Here we use the Fossilized Birth-Birth Death process implemented in BEAST v 2.4 to estimate the divergence time of the uniformly terrestrial Cyclophoroidea (Mollusca: Caenogastropoda) from the rest of the Caenogastropoda. Our analysis shows that the terrestrialization of the Cyclophoroidea occurred around the end of the Paleozoic, and may have been associated with the End Permian mass extinction. This places the Cyclophoroidea as the first caenogastropod clade to make the transition to terrestriality.

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