Coryphodon and the Paleocene-Eocene Thermal Maximum: Emily Randall’s Senior Independent Study thesis

Editor’s Note: Independent Study (IS) at The College of Wooster is a three-course series required of every student before graduation. Earth Sciences students typically begin in the second semester of their junior years with project identification, literature review, and a thesis essentially setting out the hypotheses and parameters of the work. Most students do fieldwork or labwork to collect data, and then spend their senior years finishing extensive Senior I.S. theses. This year we have the COVID-19 pandemic to deal with in the spring, so our students have not had a chance to publicly present their hard work and scientific ideas. Some, then, will be writing blog posts like this. The text and images below are from Emily Randall (’20) who participated in a Keck Geology Consortium project last summer. The picture above shows Emily on the right in Wyoming (with Isaac and Mike) collecting Coryphodon teeth. And now Emily takes over —

Abstract

Preliminary data point toward a new hypothesis in which Coryphodon lived in wetter habitats before the Paleocene-Eocene Thermal Maximum (PETM), but was able to adapt to drier habitats in order to survive post-PETM. Early Paleogene nonmarine strata are extensively exposed in the Bighorn Basin of northwestern Wyoming. The Fort Union and Willwood Formations represent alluvial deposition within a Laramide Basin formed from the Paleocene through early Eocene. Therefore, the basin is an ideal place to study the local effects of the PETM, a rapid global warming event that occurred about 55.5 million years ago at the Paleocene–Eocene boundary. During this event, an initial decrease in rainfall was followed by wet and dry cycles with increased temperature and decreased precipitation. Some flora and fauna went extinct, but many others exhibited dwarfing during this interval. The response of the large mammal Coryphodon to the PETM is poorly understood, but is of special interest due to its inferred semiaquatic nature.

We collected 14 stratigraphic sections from 5 mammalian biozones within the Bighorn Basin, each centered around depositional units containing Coryphodon. The depositional environments of these units were evaluated by describing the grain size; matrix and mottling colors; mottling percent; abundance and type of nodules; shrink-swell features such as slickensides and clay cutans; and other interesting attributes such as organic matter, invertebrate fossils, sedimentary features, and mottling color or percentage stratigraphic changes. The depositional environments include ponds, swamps, fluvial deposits, soils with evidence of wet and dry cycles, and dry soils.

Reflection

Completing my independent study was an extremely rewarding process and I am so happy I was able to have this experience. I was lucky enough to be part of a larger Keck Geology Consortium project, which allowed the team to tackle many more research questions than just one student project ever could. We spent about a month in the Bighorn Basin in northwestern Wyoming collecting data over the summer before I began working on my independent study on campus. It was amazing to be able to gain so much field experience and get to work with such a great team! Back on campus, I was able to focus on data analysis and teaching myself Adobe Illustrator in order to create stratigraphic columns. And then, of course, there was a lot of writing, reading, thinking, and analysis to do to complete my independent study. In the end, I am very proud of how my stratigraphic columns and independent study turned out!

Stratigraphic columns from Clarkforkian (Cf) 2 and 3 mammalian biozones (Pre-PETM).

Some of the Keck Wyoming team collecting Coryphodon fossils. From top to bottom left and then top to bottom right, Michael, Richard, Grant, Simone, Danika, Isaac, and Emily.