Date of Award

August 2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Geosciences

First Advisor

Margaret L. Fraiser

Committee Members

John L. Isbell, Peter M. Sheehan, Mark T. Harris, Stephen Q. Dornbos

Keywords

Community Structure, Functional Diversity, Marine Invertebrate, Permo-Triassic Mass Extinction, Restructuring

Abstract

The Permo-Triassic mass extinction (PTME) was the largest biodiversity collapse in Earth’s history. Published data has been interpreted as indicating that marine ecological devastation following the PTME was protracted and may have lasted 5 million years into the Middle Triassic (Anisian). However, a review of previous literature shows that understanding of biotic recovery is usually based on only a few components of the ecosystem, such as on taxonomic diversity, a single genus/phylum, or shallow water facies. Typically, paleocommunities are considered fully recovered when dominance and diversity are regained and normal ecosystem functioning has resumed. However, to more fully characterize Triassic ecologic restructuring, paleoecologists should take into account ecological proxies, such as functional diversity and marine paleocommunity structure. Functional diversity (i.e., richness and evenness), defined as the abundance and distribution of traits present in a community, has important implications for the functioning of ecosystems in the wake of events of major disturbance. Function richness and evenness was quantified from two post-PTME marine localities (i.e. south China, and the western United States), in addition to previously published datasets using a ten-trait ecospace model. Data from marine fossil assemblages in all of these localities indicates that paleocommunities had high taxonomic diversity and generally high functional richness, but appear to be functionally uneven. The two case study paleocommunities, the Spathian Virgin Limestone and Anisian Leidapo Member, were numerically and ecologically dominated by one functional group, implying that either resource availability and/or the utilization of resources in these post-extinction paleocommunities was uneven, or strong environmental filtering was in effect. As such, despite deposition in fairly stable ramp paleoenvironments, both of these biotic assemblages would have been very susceptible to biotic and environmental perturbations such as recurrent species invasion or anoxic events. While it is uncertain whether this pattern is typical of all paleocommunities in the aftermath of the PTME, these results imply that some Early and Middle Triassic paleocommunities may not have been as fully restructured as previously thought, and could have been inherently unstable due to the numerous biotic and environmental changes present in the wake of the PTME.

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