Siobhán Cooke is an assistant professor of functional anatomy and evolution. Her research focuses on the evolution and eventual extinction of the native mammals of the Caribbean region. She also teaches human anatomy to medical students. On Dec. 11, 2017, Cooke joined Reddit’s Ask Me Anything and answered questions on paleontologists’ obsession with teeth and why they often teach anatomy to medical students
Why do paleontologists care about teeth so much?
Cooke: Teeth are hard—enamel is the hardest substance in the body—so they preserve very well in the fossil record, and they are often very distinctive of and unique to the species.
Teeth also reflect the diet of an animal. Since changes in diet often lie at the root of evolutionary changes and transitions, dentition can give researchers a window into change through time. In other words, you can learn a lot about an organism’s ecological niche by understanding their diet.
You can also extract stable isotope data from teeth. For example, oxygen stable isotopes can provide information about climate, carbon can shed light on if the organism was consuming C4 or C3 vegetation (i.e., grasses versus other types of plants such as oak trees) and nitrogen isotopes can tell you about trophic level.
Finally, sometimes fossils contain DNA, and many researchers are now using ancient DNA to better understand the relationships between extinct animals and their living relatives.
What can modeling tell you about teeth, and how does this information relate to human teeth?
Cooke: By modeling how dentition processes food items, we can understand what food that animal may have eaten.
For human dentition, dental modeling has been used to understand different dietary transitions through evolutionary time. Our very early human ancestors, Australopithecus, had relatively large teeth for their body size compared to what we see at a later date in human evolution. The dental morphology as well as isotopic data indicate that they were eating a largely vegetarian diet of fruits and leaves. Larger teeth are more resistant to wear that would have been caused by these food types.
Once the earliest members of our own genus, Homo, evolve, we start to see a decrease in overall tooth size. This probably signals a transition to foods that were easier to process (e.g., meat). When Homo sapiens come on the scene, we get lots of extra-oral food processing such as cooking, which further decreases selective pressure to maintain a large set of chompers.
Siobhán Cooke answer questions during her reddit/AMA
Are teeth really that helpful as a fossil?
Cooke: Yes. They are both helpful and what is there. No paleontologist is going to turn down finding more than just the teeth, but beggars cannot be choosers.
What does this have to do with teaching medical students?
Cooke: Paleontologists are often trained in anatomy because we reconstruct anatomy of extinct animals, which is key for understanding the anatomy of the human species. Many of the faculty members in the Center for Functional Anatomy and Evolution are functional anatomists with a paleontological component to their research. During the summer and fall, we bring our anatomical knowledge into the classroom to help train the next generation of doctors at the Johns Hopkins University School of Medicine. In the lab, it is really exciting to be able to talk with students about how the evolutionary history of our own anatomy can affect health today.
While most of our teaching is to medical students, we also run a summer anatomy institute for undergraduate students where cadaveric dissection is a component—just like in a medical school gross anatomy class.
If you could bring back any extinct animal, which one would it be and why?
Cooke: Everyone always wants to bring back extinct animals, and I understand the impulse, but I would rather see any money that would go into reintroducing extinct animals go to modern conservation efforts. We are facing the sixth mass extinction, and there are lots of animals that are almost walking ghosts. Genetic diversity is declining, habitat is disappearing. All of our efforts should be going into preserving what is still able to be saved. I understand the impulse to want to bring things back, but I am a bit of a realist toward our limited grant resources.
However, it is definitely fun to think about what extinct animals would have been like. If I were to choose, I would like to see the ground sloths, as they are so different from anything living today. It would be interesting to know their feeding behaviors and how they might have modified their environments.