Graduate Studies

 

First Advisor

Peter J. Wagner

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Geosciences

Date of this Version

8-2024

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Earth and Atmospheric Sciences (Geology)

Under the supervision of Professor Peter J. Wagner

Lincoln, Nebraska, August 2024

Comments

Copyright 2024, Katherine Jane Jordan. Used by permission

Abstract

Ecological disruption events such as mass extinctions can result in the permanent alteration in clades and ecosystems. A pivotal time of change during the history of life on Earth can be seen in the Devonian Period. During this time, major transitions in marine and terrestrial system resulted in a different world at the end of the period in comparison to the beginning. One such group most heavily impacted were trilobites. Trilobites were reduced to one order by the end of the Devonian: Proetida. My dissertation focuses on phylogenetic, biogeographic, and paleocommunity patterns of this group, known as the last of the trilobites. In my first chapter, I produce a more comprehensive global phylogeny for this order from the Devonian to the early Carboniferous. Upon completing a Bayesian phylogenetic analysis using the FBD-model, I find that the relaxed-clock model has an overall higher probability. Additionally, many groups once considering monophyletic, like Gerastos, are resolved as polyphyletic and may be based on morphological types rather than relatedness. Following this, in my second chapter, I incorporate a dispersal parameter into an FBD-model (the FBDMM model). When comparing the FBDMM tree to the FBD tree from chapter 1, both trees are very similar and the dispersal parameter “fine-tuned” the original tree. Lastly, in chapter 3, I look at the paleocommunity assembly patterns of proetides with another trilobite order, Phacopida, and brachiopods across the Devonian. I used both co-occurrence analysis and follow this with the Modified Pairs Analysis to statistically test abiotic variables contribution to co-occurrence patterns. I find that aggregations decrease during the middle Devonian and return during the end-Devonian. Additionally, of all the abiotic factors examined, only distance (longitude and latitude) was significant in impacting aggregated pairs. This may indicate other factors, both abiotic and/or biotic, not included in this study may be partially responsible for pair associations in the Devonian.

Advisor: Peter J. Wagner

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