Taxonomic Revision and Intraspecific Variation Among Early and Middle Eocene Rodents from the Green River Basin, Bighorn Basin, and Lost Cabin of Wyoming

Name: Brieanne Oehlke
Year of Graduation: 2010
Hometown: Fremont, WI
Major: Biology (Biomedical Science)
Minor: Chemistry

Name: Dr. Deb Anderson, Associate Professor of Biology
Research Specialty: Paleobiology

Ischyromyids are some of the earliest rodents to show up in the fossil record.  Many of them lived from the Early to Middle Eocene (55-52 mya) in the Bighorn Basin and Green River Basin of Wyoming.  Being some of the first rodents to evolve, their molar crown pattern is simple (i.e. four cusps with cingula and some crests), yet distinctive.  Over time, minor changes in the crown pattern occurred, producing a number of new rodent species.  Since the ischryomyids are the base group, the molar crown pattern for other rodents can be derived from the basic four cusp pattern.  This makes it difficult to differentiate among species within the family Ischyromyidae.  This project works to clarify the taxonomic classification of Paramys delicatus and P. delicatior, which are common species found at both the Bridger and Willwood formations of Wyoming.  In the past, workers have reported new specimens of these taxa, but have not compared the populations to look at geographic and intraspecific variation among them. By documenting these two categories of variation, we can clarify the alpha taxonomy of these two species, making them more useful for future biostratigraphic correlations.

The ultimate goal of this project is to:

            (1)  Revise the alpha taxonomy for Paramys delicatus and Paramys delicatior.

            (2)  Describe size and/or morphological changes in crown pattern over time.

            (3)  Document geographic variation in the two species

The major reason I became interested in undergraduate research was make myself more competitive when applying to Dental Schools.  I had known since I was in high school that I wanted to be a dentist.  When I started my Freshman year of college I was finding ways to do anything I could to build my resume.  By my Junior year the one thing I was lacking was being involved in research.  I had Dr. Anderson for General Biology II my sophomore year and knew that she was doing research on rodent teeth; I did not know any details or what the research was about, but I knew I wanted to be a part of her research specifically.  I knew there were other research opportunities I could have engaged in, but I was immediately interested in research involving teeth.  I knew this would be beneficial for not only my career, but also for learning research techniques as an undergrad.

From this research on rodent teeth I have learned so much in a short amount of time.  I have learned that slight differences in molar size and morphology can really make a difference when differentiating between two different species.  I have learned different terminologies for the shape of a tooth or molar and the different cusps and characteristics that different molars have, which can be very helpful for my future at dental school when I'm learning about human teeth.  Through this research I feel more confident in my ability to go through readings and grasp the main idea that the author is trying to convey, I am advanced in taking measurements of teeth and being able to compare those measurements and qualitative data with other rodents, and I am also more confident in my overall ability to conduct research.

What I value most about my undergraduate research experience is the fact that I got to participate in something more than just the usual lectures and labs that every other biology student does.  I got to participate in something that has not been looked at since 1962 by any one person around the world and that is something really rewarding to be a part of.   This research has helped me to prepare for dental school and my career by giving me extra knowledge about teeth that I would not have known about otherwise.  This experience contributed to my knowledge and understanding of mammalian dental morphology and variation.  Lastly, the hands on experience is the best way to learn the scientific process, and the interaction between student and faculty allows for students to be guided while experiencing the gains and hardships of conducting research.

Specimens of the two species from both the Bighorn and Bridger Basins increase in size over time, coincident with cooling of the local climate.  By documenting this size change in specimens from two distinct geographic regions, Brie and I are facilitating taxonomic identification of specimens recovered in the future.  Brie is very insightful in her approach to identifying significant qualitative features of the molars.  This work is being supported by a grant from the Student-Faculty Endowment Fund.  Our results will be presented at the 2010 Day of Celebration at St. Norbert College.