The American Bison is a fearsome animal that can stand up to 6 ft and over 2000 pounds, with females being a bit smaller than the males. They are a very strong animal that even predators can be scared to hunt for fear of an injury, but humans have commonly hunted them. Even without the use of guns, many hunters using bow and arrows were able to still fell the American Bison. This is due to their unique respiratory system, where they are the only animals that the lungs share the same pleural cavity (Palmer et al., 2025). This leads to a human hunter only having to aim for the pleural cavity to collapse the whole system for the American Bison, while another animal will have only one lung collapse and have a slight chance of surviving because they still have one functioning lung. The lack of separated lung cavity led them to be very susceptible to respiratory diseases, such as a variation of the coronavirus, and anything that could target their more delicate system (Palmer et al., 2025). Humans also almost hunted this bison to extinction because all they had to target was the bison’s chest with a gun or bow to fell it.
Why would the American Bison evolve to have this feature? Well this isn’t exactly known, with the leading theory being that it was simply how the lungs developed to compensate for the size and other assets the bison went for (Oppenheimer, 2021). There doesn’t seem to be any clear advantages to this lung system, or any environmental reasons for it. The other problem is that humans hunted the bison so much that the sample size and environment diversity has lessened. Understanding these unique physiological evolutions is very important, and conservation efforts to keep these animals alive are key to understanding.
Resources
Palmer, M. V., Buckley, A., Cassmann, E. D., Olsen, S. C., Nielsen, D. W., Putz, E. J., Seger, H., Chandler, J. C., & Boggiatto, P. M. (2025). Permissiveness of American bison to infection with severe acute respiratory syndrome coronavirus-2. Scientific Reports, 15(1), 1–11. https://doi-org.dml.regis.edu/10.1038/s41598-025-10100-3
Oppenheimer, J., Rosen, B. D., Heaton, M. P., Ley, B. L. V., Shafer, W. R., Schuetze, F. T., Stroud, B., Kuehn, L. A., McClure, J. C., Barfield, J. P., Blackburn, H. D., Kalbfleisch, T. S., Bickhart, D. M., Davenport, K. M., Kuhn, K. L., Green, R. E., Shapiro, B., & Smith, T. P. L. (2021). A Reference Genome Assembly of American Bison, Bison bison bison. Journal of Heredity, 112(2), 174–183. https://doi-org.dml.regis.edu/10.1093/jhered/esab003
Hi Noel!
ReplyDeleteWow I did not know this and this is so cool! While reading I did wonder why Bisons would not evolve from the lack of a mediastinum but that makes sense! I was curious and searched up other animals with a “disadvantage” as such and found out that elephants—one of my favorite creatures—have no pleural space! The space is instead connective tissue, and therefore they are the only mammal that can snorkel at depth (West, 2002). Although they have a normal pleural space at the fetal stage that obliterates to connective tissue through gestation. This is thought to protect the lungs against spontaneous pneumothorax when the animal raises water through its trunk. I am sure these adaptations have been made due to the elephants aquatic nature as well. But it is interesting to see that both mammals have almost inexplainable anatomies and seem to be living—for the most part—just fine.
West, J. B. (2002). Why doesn’t the elephant have a pleural space? Physiology, 17(2), 47–50. https://doi.org/10.1152/nips.01374.2001