Date of Completion

6-13-2018

Embargo Period

12-31-2018

Advisors

Dr. Andrew Bush, Dr. Morgan Tingley, Dr. Lisa Park Boush

Field of Study

Ecology and Evolutionary Biology

Degree

Master of Science

Open Access

Open Access

Abstract

Mass extinctions are often associated with multiple environmental perturbations. For example, the Upper and Lower Kellwasser Events (the two pulses of the Frasnian-Famennian mass extinction in the Late Devonian) coincide with both global cooling and ocean anoxia/dysoxia. Assessing the selectivity of extinction—which types of organisms survived versus died—can help constrain which environmental changes were most important as kill mechanisms. Here, selectivity is examined with respect to several factors during the Lower Kellwasser Event. A thick package of siliciclastic sediments was deposited in the Appalachian Foreland Basin during the Late Devonian. Thanks to recent stratigraphic revisions, the Kellwasser Events can be traced along a paleoenvironmental gradient that shallows from west to east in New York and northern Pennsylvania. Previous studies have shown that brachiopod species composition varies significantly along this gradient, and that the Lower Kellwasser Event was the more severe of the two extinctions. The Wiscoy Formation was targeted for this study as it immediately predates the first extinction pulse. We collected bulk samples from numerous localities along the paleoenvironmental gradient and identified 7,933 brachiopod fossils from 21 genera and 26 species. Non-metric multidimensional scaling was used to quantify variation among species in environmental preference; variation in extinction intensity among habitats could indicate that anoxia was a kill mechanism, because oxygen levels likely varied with depth. Brachiopod orders varied in latitudinal distribution in the Devonian, so variation in extinction intensity among orders could implicate cooling as a kill mechanism. We also tested the effects of abundance and body size on probability of extinction. Multiple logistic regression strongly supported global cooling as a major kill mechanism—species belonging to orders prevalent at low latitudes had higher probability of extinction than those belonging to orders common at high latitudes. In contrast, paleoenvironmental preference was not a major predictor of extinction in these data.

Major Advisor

Dr. Andrew Bush

Available for download on Monday, December 31, 2018

Share

COinS