Paleoenvironments Containing Coryphodon in the Fort Union and Willwood Formations Spanning the Paleocene-Eocene Thermal Maximum (PETM), Bighorn Basin, Wyoming

Student: Emily Randall
Major: Geology
Minor: Environmental Studies
Wooster Advisor: Dr. Mark Wilson, Dr. Karen Alley
Keck Advisors: Dr. Michael D’Emic, Dr. Simone Hoffmann, Dr. Brady Foreman

Preliminary data point toward a new hypothesis in which Coryphodon lived in wetter habitats before the Paleocene-Eocene Thermal Maximum (PETM), but adapted to drier ones post-PETM. The Fort Union and Willwood Formations in the Bighorn Basin of Wyoming represent alluvial deposition within a Laramide Basin formed from the Paleocene through early Eocene. This is an ideal place to study the local effects of the PETM, a rapid global warming event that occurred at the Paleocene–Eocene boundary (~55.5 mya). 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 basin, each centered around depositional units containing Coryphodon. The depositional environments of these units were evaluated through sedimentary analysis, and included ponds, swamps, fluvial deposits, soils with evidence of wet and dry cycles, and dry soils.

I have been interested in paleontology since high school, and for my I.S. I was lucky enough to be selected to be part of a wonderful Keck Geology Consortium research team focused on paleontology in the Bighorn Basin, Wyoming. Keck is a group of seventeen small liberal arts colleges that receives support from the National Science Foundation to run research programs for geology undergraduate students every summer. My project was a year-long, but it will continue with other researchers in the future. Each of the six students in the program had an individualized research project centered around Coryphodon, a large hippo-like mammal, that lived during the Paleocene-Eocene Thermal Maximum (PETM), which was a rapid global warming event that occurred about 55.5 million years ago.

Since I was interested in seeing how this interval of warming and drying would affect the paleoenvironments that the previously-hypothesized to be semi-aquatic mammal lived in, my project focused on sedimentary analysis to reconstruct the paleoenvironments our fossils were found in. It was very rewarding to expand my knowledge of paleontology and sedimentology and stratigraphy through fieldwork and research during my I.S. experience. I thoroughly enjoyed the whole I.S. process, and it solidified my love of fieldwork, research, and the western United States.

Emily will be online to field comments on May 8:
10am-noon EDT (Asia: late evening, PST 6am-8am, Africa/Europe: late afternoon)

22 thoughts on “Paleoenvironments Containing Coryphodon in the Fort Union and Willwood Formations Spanning the Paleocene-Eocene Thermal Maximum (PETM), Bighorn Basin, Wyoming”

  1. Paleontology! I am proud to be one of your advisors, Emily. Excellent project with clear hypotheses and tests, and written so very well. You taught me a lot about large mammals and ancient soils. Congratulations on your accomplishments!

    1. Thank you so much Dr. Wilson, that means a lot to me! It was wonderful to have you as an advisor and I have learned so much from you!

  2. Emily, what is the significance of discovering that Coryphodon apparently adapted to a shifting environment?

    1. The PETM has been used in a lot of areas as an analog for the possible impacts of modern climate change, as the warming appears to have been mainly driven by carbon dioxide. Therefore, seeing that Coryphodon was able to adapt to, and actually live in, much drier environments after the PETM may show that modern large mammals could also adapt to live in drier environments caused by future global warming.

      A good publication on how these two events compare was published by Gingerich in 2019 and is titled “Temporal scaling of carbon emission and accumulation rates: modern anthropogenic emissions compared to estimates of PETM-onset accumulation”.

  3. Great job, Emily! You explained your research lucidly, and your curiosity and diligence really shine through. I was wondering if you were surprised by your results. Also, do you have any idea of long the coryphodon survived after the PETM?
    I hope you’re proud of all your fantastic achievements!

    1. Hi Cara, thank you so much for your kind words.
      I was surprised at how sharp the contrast was between the pre-PETM and post-PETM paleoenvironments that Coryphodon lived in. I was originally expected to find them mainly in aquatic or semi-aquatic environments on both sides of the PETM, and thoroughly expected there to be at least be a few specimens found in these types of environments after the PETM, but there were none. That said, my sample size was quite small, so more samples really need to be collected to see if this observation holds up.
      Coryphodon went extinct in the early Eocene, so roughly a few million years after the PETM.

  4. Hi Emily! Excellent project! Thanks for showing us how the soil morphology index helps you make your paleoenvironmental interpretations. Do you think the soil morphology index would be a useful skill to learn in Earth Materials?

    1. Hi Dr. Pollock! As far as I know, the soil morphology index has only been used in the Bighorn Basin, as it was created for this area by Adams et al. However, it seems like a system that could be pretty easily adapted to paleosols in other areas.

  5. Thank you so much Dr. Wilson, that means a lot to me! It was wonderful to have you as an advisor and I have learned so much from you!

  6. Awesome work, Emily! Do you have any advice for younger students interested in getting involved in field research?

    1. Hi Dr. Faust! I would definitely say start talking with your professors and looking for programs like Keck early on. Even if you don’t start out doing a larger research project, you’ll get some field experience and, once you have your foot in the door, it’s much easier to find more field research opportunities because you have some experience.

  7. Are there changes in the fossils of Coryphodon across biozones that may support your conclusions that they became less aquatic?

    1. That’s a good question, and I’m interested to see if that might be the case as well. A couple of my Keck teammates are focusing more on analyzing the bones and teeth of Coryphodon that we found. So I’m hoping that when we all share our final posters I may gain more insight into this.

      1. I should also note that there has been previous research into Coryphodon dwarfing during the PETM, but I have yet to see if our specimens also follow this trend.

  8. Hi Emily–congratulations on this fascinating project! My question connects to Karen Havholm’s and Frank Samuelson’s. Granted that this may be outside the scope of your research, but do you have a sense of how Coryphodon itself changed across the changes in climate (in morphology or behavior), and/or how the varied ecosystems it was a part of functioned?

    1. Previous research has shown that Coryphodon in the Bighorn Basin dwarfed during the PETM, as did early horses in this area. However, a lot of the research into Coryphodon is old and the fossils are often not linked with their sedimentological data, mainly because the paleontologists who study this area now are much more interested in small mammals such as early primates. I’m interested to see how the research of some of my Keck teammates, who are looking more at the morphology of the Coryphodon specimens we found, aligns with what I found with respect to Coryphodon’s changing paleoenvironments.

  9. Hi Emily,
    It’s great to visit the Symposium today and learn about the work you have been doing this year in IS. Thank you for sharing your work here, and congratulations on a job well done!
    🙂

  10. Nice job Emily and congratulations on the internship. Why did these great animals go extinct?

  11. Hi Emily–

    So proud of you for doing a virtual presentation at IS Symposium. Can I tell you that I love the PETM? Anything about the Paleocene-Eocene is something that always catches my interest. (Because, you never know, even though you were in Wyoming, I can take your knowledge with me into my home base of Utah. Most of the rocks that I am interested in span the PETM!!). Also, I hear that you might be stomping around in the Green River Formation after graduation from Wooster? You know how I love the Green River — I’m in a smaller basin of the Green River every summer, not the “big boys” of Lake Gosuite or Lake Uinta that are more well known.

    Again, great job finishing IS, doing this Symposium, and for finishing finals this week. -SJ

  12. Beautiful poster, Emily! I’m wondering if you think your research into Coryphodon could be used to predict the reactions of modern large mammals to modern climate change. I know the small sample size is a significant limitation here, but with more research and sampling in the area, could we use Coryphodon as an analogy to what could happen to modern mammals, such as hippos, with future warming? Or are the differences between the PETM and modern climate too great to make this comparison? Congratulations, and great job!

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