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theses

Evolution is the process by which species change through time, and understanding the evolutionary processes that occur today allows us to infer the evolutionary history of organisms from the distant past. In this thesis, the evolutionary processes and adaptations of two distantly related organisms that inhabit different environments were studied. Chapter one investigated the size variation in pentaliths of Braarudosphaera bigelowii, a marine haptophyte that is abundant in the Lower Paleocene Zumaia section of northern Spain, and explored the idea that the variability in pentalith size represents pseudo-cryptic speciation. A cluster analysis in RStudio (mclust package) yielded two size groups, which were interpreted as two unique pseudo-cryptic species: form X (< 4.5 μm) and form Y (≥ 4.5 μm). In addition, a sudden increase in B. bigelowii abundance occurred near the Paleocene C27n/26r magnetic reversal and formed a “peak acme” zone of approximately four meters. Isotopic analyses of organic matter revealed that the onset of this acme coincided with an abrupt negative excursion (3.5‰) in δ13Corg. Biostratigraphic correlation between the Zumaia section and the Danian/Selandian boundary section at Qreiya, Egypt confirmed that this isotopic shift correlates with a hyperthermal event (Latest Danian Event), and suggests that changes in the climate may have affected the abundance of B. bigelowii at Zumaia. Chapter two described a new species of aquatic belostomatid insect, Triassonepa solensis, from the Upper Triassic, lacustrine Cow Branch Formation that outcrops along the Virginia/North Carolina border. It was placed in a new genus due to the unique structure of its raptorial foreleg, in which the tarsus is elongate and opposed to the tibia + femur. Due to the exclusive preservation of terrestrial adult insects and surface-dwelling aquatic insects, in addition to the geochemistry of the deposit, it is likely that the Cow Branch Formation was a saline, alkaline, rift valley lake.

ETD_7775

M.S.

Includes bibliographical references

by Julia A. Criscione

doi:10.7282/T34170GM

ETD graduate

The author owns the copyright to this work.