Rhinos are an amazing group of animals, and have a rich fossil history, too. During the past 40 million years, they have transformed from fairly small ancestral forms to big beasts exceeding 2,000 kg in body mass. These changes, of course, have biological consequences. An animal’s skeleton has to support that weight, but the shape of the skeleton is constrained to some extent by ancestral “baggage.” A rhino has to work with the genetics it has–so rather than getting an ideally engineered skeleton built from scratch, it has a “good enough” frame adapted from the ancestral body plan.
In humans, our modifications from smaller, non-bipedal ancestors are linked to all sorts of medical conditions. For instance, our vertebral column wasn’t ancestrally carried upright all of the time–a fact which contributes to lower back pain and arthritis, among other problems. Given massive changes in the rhino body plan over time, it stands to reason what we should see changes in their medical condition, too. If a big animal evolved from a smaller ancestor, you might predict that the big animal could be susceptible to joint problems, because its body plan wasn’t perfectly adapted for the extra weight.
A new study by Kelsey Stilson and colleagues investigates this topic, using a sample of hundreds of bones from six extinct rhino species of various body sizes, as well as modern black rhinoceros. The authors documented anomalies along joint surfaces (e.g., the joints between individual toe bones), and mapped their distribution across the various species. As predicted, larger rhinos generally show more joint issues (although other factors, such as locomotion style and habitat, may be involved too). So, any “positive” of being bigger, or changing locomotion styles, or whatever, has accompanying costs in skeletal wear-and-tear. This is a pretty cool paper (freely available in PLOS ONE, too!), and a great example of how large samples of fossils in museum collections are important for studying big evolutionary patterns.
Beyond the results themselves, there is a lot of interesting backstory to the work. So, I got in touch with Kelsey Stilson, now a Ph.D. student at University of Chicago, to learn more. My questions (in bold italics) and her answers (in plain font) are below.
There are a lot of groups you could study for paleopathology. Why rhinos?
As an undergraduate, I was lucky enough to be in the Hopkins and Davis Paleontology Labs at the University of Oregon. When I first joined I didn’t even know the difference between an astragalus and a calcaneum. So when a graduate student brought up mammalian postcranial fossils for a lab meeting I asked what all the “bloopy stuff” was on a large bone. My advisers made the mistake of telling me it was arthritis and I was hooked. As a runner and former premed, bone pathologies have always been a special passion of mine.
Rhinos turned out to be a great study system because there are a TON of them in the mid-Cenozoic and they tend to die in clusters. They are also rather charismatic, so many museum collections have decades-worth of fossil rhinos collected from field work, hunting expeditions (when that was legal), and zoo specimens. Still, I had to visit four different museums to collect enough data (and I have plans to collect more in the future).
Because this paper originated as an undergraduate research project, what special challenges did that present?
Collecting scientific data was an entirely new adventure I would recommend to anyone. It was stressful and time consuming, but then, so are most worthwhile tasks. As an undergraduate with limited experience, I made a lot of mistakes, had to recollect data a couple times, reanalyze other bits, and learned the pain of not backing up my files. The best advice I can give to current undergraduates is to always document your data collection. Take as many pictures as possible, because you never know what you will need in the future as you learn more about your study system.
I am told that you did the artistic reconstructions of the rhinos in the paper. Figure 1 (above) is pretty awesome as a snapshot summary of rhino evolution–how did you come up with the design for that?
Thank you! The final figure is a modified version of a poster presentation I gave at a Society of Vertebrate Paleontology meeting. I needed a way to convey the difference in mass of the different lineages and my advisers were unimpressed with the spheres I drew at first. I’ve always enjoyed drawing, so I spent a couple afternoons in the library researching rhino morphology and then drawing them up. If you look closely, you can see they each have separate personalities. This was not a scientific choice, but a small attempt to help the reader feel what I do when I see rhino fossils and cladograms.
I am a firm believer in the confluence of art and science. I’ve even made an outreach coloring book for the University of Texas Jackson School of Geosciences, and I’ll make paleontology logos on request.
I saw that you put your data–photos, observations, etc.–on MorphoBank. That’s awesome for the field, but must have been a ton of work. What tips do you have for other researchers who might want to follow in your footsteps and upload their own massive data sets?
Yes, it was a ton of work, but as a scientific community we have to upload everything we have (including metadata and associated documentation) for the future. Floppy discs degrade, computers crash, and notebooks get recycled. Even NASA accidentally erased the original Apollo 11 mission recordings. No matter how sloppy or out of focus you think your data is, it might be important some day and at the very least no one will have to redo that work again. My advice is to let any insecurities go and upload your data. That way there are at least two copies of it in the world. Also, include the specimen number when you rename your photos. That will save you a lot of grief.
What’s your favorite fossil out of all the ones you looked at during the research? What’s cool about it?
Favorite rhino fossil… this is going to be dorky, but it’s that first one I saw as an undergraduate. One question about that fossil inspired not just this current project, but a couple others I am still working on. The Ashfall Rhino Beds come in at a close second.
Thanks, Kelsey, for taking the time for this interview! You can learn more about her work here, or check out her blog with Brianna McHorse at Fossilosophy. Read the full rhino paper at PLOS ONE.
Stilson KT, Hopkins SSB, Davis EB (2016) Osteopathology in Rhinocerotidae from 50 Million Years to the Present. PLoS ONE 11(2): e0146221. doi:10.1371/journal.pone.0146221
[note: corrected post to clarify that Hyrachus is a stem rhino, not just a rhino cousin; thanks to Luke Holbrook and Kelsey Stilson for the clarifying info]