Jacob Harris and I, Mayeesha Ahmed are doing summer research at the Joseph Moore Museum, supervised by museum director Dr. Heather Lerner. We will be working with ancient DNA extracted from Giant Beaver (Castoroides ohioensis) specimens to find out as much as we can about this large rodent from the Pleistocene.
The Joseph Moore Museum is known for having the most complete (7/8) giant beaver fossil in the world! So naturally we were interested to find out more about this extinct species. The first step on our exciting mission was to dig up what others have found out about giant beavers, and we learned some pretty interesting stuff! Despite being called the giant beaver, the Castoroides’ habits were similar to that of a muskrat. They lived in ponds and lakes surrounded by swamps and fed on swamp vegetation. They were found in the Northeastern and Midwestern US as well as the Southeast (Florida and Georgia) and even as far up north as Alaska and Canada! Some experts say that unlike modern beavers, the giant beaver was not a woodcutter. However there are others who disagree. There are also questions about whether there was more than one species of giant beaver as significant physical differences could be found in the parts of Castoroides skulls such as the lamdoidal crest, basisphenoid, mesopterygoid fossa.
Lamboidal basisphenoid mesoptery-what-fossa? These were some of the difficult anatomy terms we were coming across, which was making it difficult to understand the papers pointing out these interesting differences that are so relevant to our research. Looks like we need some help…
But not to worry! We invited an expert, John Iverson, to tell us more about these structures and he very generously helped us out! We learned how to identify the distinctive parts of the Castoroides skull and take note of the differences that have been observed in the papers we read. By looking at the pictures of Castoroides dilophidus from the Pleistocene of Florida and comparing them to our Castoroides ohioensis specimens, we were able to see significant differences in their bone structures that suggest that they could have been two different species. But John pointed out that these differences could have been due to geographical range or time period in which they lived. How can we find out what it actually was? Ancient DNA analysis will tell us!
But where can we find this ancient DNA? So, the next day we did some research to find more information about where in the tooth we may be able to find endogenous DNA (DNA that belongs to the giant beaver we are sampling from, and not environmental DNA). We found out that if we remove the enamel of the tooth we could expose the odontoblasts in the pulp cavity that are likely to contain DNA. So then, we gathered all the materials we need for ancient specimen sampling: bleach and ethanol for sterilizing the workspace, gloves, wipes, dremel, tubes to collect samples in. Next, we finally started doing some hands-on work on taking samples from the specimens. But we had to be very careful in order to minimize risks of contamination. We are going to pack these samples up and take them with us to Michael Hofreiter’s ancient DNA lab in Germany for extraction! We also extracted modern beaver DNA, which was done in our own lab.
Because of it’s age and many environmental factors, ancient DNA is very difficult to extract. I am really hoping that our samples contain DNA we can use for analysis and I am looking forward to learning more about ancient DNA in Germany