Painting a New Perspective on Ordovician Echinoderm Diversity Patterns

Graduation Year

2024

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Geology

Major Professor

Sarah Sheffield, Ph.D.

Committee Member

Joni Firat, Ph.D.

Committee Member

Adriane Lam, Ph.D.

Committee Member

Ping Wang, Ph.D.

Keywords

Biodiversity, Echinodermata, Extinction, Paleontology, Paleozoic

Abstract

The Ordovician Period was a time of great biotic and environmental change, encompassing two important biotic events: the Great Ordovician Biodiversification Event (GOBE) and the Late Ordovician Mass Extinction (LOME). The GOBE occurred during the Middle Ordovician and was a period of rapid diversity increase for marine invertebrate groups, as lower-level taxonomic groups like families and genera came into the forefront. The Ordovician ends with the LOME, an extinction event that is thought to have occurred in two phases: an initial glaciation followed by a subsequent warming. Approximately 85% of marine species went extinct during the LOME, making it the second most severe extinction in Earth’s history. An important area of paleobiological research involves investigating how various fossil groups responded across these biotic events. Echinoderms are an excellent model system with which to test hypotheses of biodiversity dynamics because they are temporally expansive, globally distributed, and have a rich evolutionary history. Despite this, our current understanding of Paleozoic echinoderms’ biodiversity patterns is not well constrained, as many studies either focus on crinoids, a highly speciose and well-documented group, or lack a finer temporal resolution. To remedy this, we examined the patterns of diversity of all major classes of echinoderms, represented by 366 globally distributed genera. After collecting the temporal ranges and geographic distributions for these genera, we calculated their rates of generic diversity, origination, and extinction at a rate of 1 Ma. Doing so revealed patterns of biodiversification unlike those in previous analyses of echinoderm diversity. Our recovered patterns of diversity revealed a two-stepped GOBE and a three-stepped LOME, both of which are patterns distinct from previous interpretations of these events. Based on the geographic range of our data, our three-stepped LOME also contributes to a growing body of research that indicates the LOME was truly a three-phased, as opposed to a two-phase, extinction event.

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