PHD, Kent State University, 2022, College of Arts and Sciences / School of Biomedical Sciences

Having transitioned from a terrestrial lifestyle to an aquatic one over roughly 50 million years, cetaceans (whales, dolphins, and porpoises) make for prime subjects of study of respiratory and olfactory anatomy. As obligately aquatic mammals, they are often considered to have reduced olfactory anatomy. Here, I provide evidence that baleen whales have retained this anatomy, and toothed whales lack olfactory anatomy. In reconstructing the upper respiratory tracts of prenatal dolphins from computed tomography, I document the anatomy of the air sacs, pterygoid sinus systems, and asymmetries thereof. Olfactory anatomy was absent. However, in bowhead whales (Balaena mysticetus), a species of baleen whale, nasal chambers and turbinates were visible in prenatal development. I describe and clarify the anatomy within their nasal chambers. Olfactory epithelium, identified histologically, covers the dorsalmost and caudalmost corner of the nasal chamber, including some of the ethmoturbinates. I identify olfactory epithelium using explicit criteria of mammalian olfactory epithelium. Immunohistochemistry revealed the presence of olfactory marker protein, which is only found in mature olfactory sensory neurons. Although it seems that these neurons are scarce in bowhead compared to typical terrestrial mammals, our results suggest that bowheads have a functional sense of smell, which they may use to find prey. The closest living relatives of cetaceans are artiodactyls, even-toed ungulates, such as sheep, camels, and giraffes. I used Cetartiodactyla, the clade that comprises artiodactyls and cetaceans, as the taxon to test the relationships found in Bird et al. (2018). They found that once body mass and phylogeny are accounted for, it is possible to use the surface area of the cribriform plate to predict the number of olfactory receptor genes that fossil mammals have. I confirmed their results and predicted gene counts in fossil whales, thereby documenting a decrease in (open full item for complete abstract)

Committee: J. G. M. Thewissen (Advisor); Samuel Crish (Committee Member); Mary Ann Raghanti (Committee Member); Edgar Kooijman (Committee Member); Tobin Hieronymus (Committee Member) Subjects: Anatomy and Physiology; Animals; Biology; Evolution and Development; Histology; Morphology; Paleontology