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Compared with other mammals (e.g., primates, rodents, and carnivores), the form and function of the ungulate nasal fossa, in particular the ethmoidal region, has been largely unexplored. Hence, the nasal anatomy of the largest prey species remains far less understood than that of their predators, rendering comparisons and evolutionary context unclear. Of the previous studies of nasal anatomy, none have investigated the detailed anatomy and functional morphology of the white-tailed deer (Odocoileus virginianus), a species that is ubiquitous throughout North and Central America and in northern regions of South America. Here, nasal form and function is quantitatively investigated in an adult white-tailed deer using high-resolution magnetic resonance imaging, combined with anatomical reconstruction and morphometric analysis techniques. The cross-sectional anatomy of the airway is shown and a three-dimensional anatomical model of the convoluted nasal fossa is reconstructed from the image data. A detailed morphometric analysis is presented that includes quantitative distributions of airway size and shape (e.g., airway perimeter, cross-sectional area, surface area) and the functional implications of these data regarding respiratory and olfactory airflow are investigated. The white-tailed deer is shown to possess a long, double scroll maxilloturbinal that occupies approximately half of the length of the nasal fossa and provides a large surface area for respiratory heat and moisture exchange. The ethmoidal region contains a convoluted arrangement of folded ethmoturbinals that appear to be morphologically distinct from the single and double scroll ethmoturbinals found in most other non-primates. This complex folding provides a large surface area in the limited space available for chemical sensing, due to the expansive maxilloturbinal. Morphologically, the white-tailed deer is shown to possess a dorsal meatus that leads to an olfactory recess, a nasal architecture that has been shown in other non-primate species to cause unique nasal airflow patterns to develop during sniffing that are optimized for odorant delivery to the sensory part of the nose. Additionally, we demonstrate that, during respiration, airflow in the nasal vestibule and the anterior maxilloturbinal region may be transitional or turbulent, in which case turbulent mixing is expected to enhance respiratory heat and moisture exchange, which could be an important contribution to thermoregulation and water conservation in the white-tailed deer. |
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