Comparative Morphology and Histology of the Nasal Fossa in Four Mammals: Gray Squirrel, Bobcat, Coyote, and White-Tailed Deer

Morphology of pig nasal structure and modulation of airflow and basic thermal conditioning

Mammals have presumably evolved to adapt to a diverse range of ambient environmental conditions through the optimized heat and mass exchange. One of the crucial biological structures for survivability is the nose, which efficiently transports and thermally preconditions the external air before reaching the internal body. Nasal mucosa and cavity help warm and humidify the inhaled air quickly. Despite its crucial role, the morphological features of mammal noses and their effect in modulating the momentum of the inhaled air, heat transfer dynamics, and particulate trapping remain poorly understood. Tortuosity of the nasal cavity in high-olfactory mammalian species, such as pigs and opossum, facilitates the formation of complex airflow patterns inside the nasal cavity, which leads to the screening of particulates from the inhaled air. We explored basic nasal features in anatomically realistic nasal pathways, including tortuosity, radius of curvature, and gap thickness; they show strong power-law correlations with body weight. Complementary inspection of tortuosity with idealized conduits reveals that this quantity is central in particle capture efficiency. Mechanistic insights into such nuances can serve as a tipping point to transforming nature-based designs into practical applications. In-depth characterization of the fluid-particle interactions in nasal cavities is necessary to uncover nose mechanistic functionalities. It is instrumental in developing new devices and filters in a number of engineering processes.

Mammalian maxilloturbinal evolution does not reflect thermal biology

The evolution of endothermy in vertebrates is a major research topic in recent decades that has been tackled by a myriad of research disciplines including paleontology, anatomy, physiology, evolutionary and developmental biology. The ability of most mammals to maintain a relatively constant and high body temperature is considered a key adaptation, enabling them to successfully colonize new habitats and harsh environments. It has been proposed that in mammals the anterior nasal cavity, which houses the maxilloturbinal, plays a pivotal role in body temperature maintenance, via a bony system supporting an epithelium involved in heat and moisture conservation. The presence and the relative size of the maxilloturbinal has been proposed to reflect the endothermic conditions and basal metabolic rate in extinct vertebrates. We show that there is no evidence to relate the origin of endothermy and the development of some turbinal bones by using a comprehensive dataset of µCT-derived maxilloturbinals spanning most mammalian orders. Indeed, we demonstrate that neither corrected basal metabolic rate nor body temperature significantly correlate with the relative surface area of the maxilloturbinal. Instead, we identify important variations in the relative surface area, morpho-anatomy, and complexity of the maxilloturbinal across the mammalian phylogeny and species ecology.

When morphology does not fit the genomes: the case of rodent olfaction

Linking genes to phenotypes has been a major question in evolutionary biology for the last decades. In the genomic era, few studies attempted to link olfactory-related genes to different anatomical proxies. However, they found very inconsistent results. This study is the first to investigate a potential relation between olfactory turbinals and olfactory receptor (OR) genes. We demonstrated that despite the use of similar methodology in the acquisition of data, OR genes do not correlate with the relative and the absolute surface area of olfactory turbinals. These results challenged the interpretations of several studies based on different proxies related to olfaction and their potential relation to olfactory capabilities.

The scaling of olfaction: Moths have relatively more olfactory surface area than mammals

Body size affects nearly every aspect of locomotion and sensing, but little is known how body size influences olfaction. One reason for this missing link is that olfaction differs fundamentally from vision and hearing in that molecules are advected by fluid before depositing on olfactory sensors. This critical role of fluid flow in olfaction leads to complexities and trade-offs. For example, a greater density of hairs and sensory neurons may lead to greater collection, but can also lead to reduced flow through hairs and additional weight and drag due to a larger olfactory organ. In this study, we report the surface area and sensory neuron density in olfactory organs of 95 species of moths and mammals. We find that approximately 12-14 percent of an olfactory system's surface area is devoted to chemosensors. Furthermore, total olfactory surface area and olfactory sensing surface area scale with body mass to the 0.49 and 0.38 powers respectively, indicating that moths have a higher proportion of olfactory surface area than mammals. The density of olfactory neurons appears to be near the limit, at 10,000 to 100,000 neurons per square mm across both insects and mammals. This study demonstrates the need for future work detailing how scaling of olfaction and other senses vary across taxa.

A comparison of diceCT and histology for determination of nasal epithelial type

Diffusible iodine-based contrast-enhanced computed tomography (diceCT) has emerged as a viable tool for discriminating soft tissues in serial CT slices, which can then be used for three-dimensional analysis. This technique has some potential to supplant histology as a tool for identification of body tissues. Here, we studied the head of an adult fruit bat (Cynopterus sphinx) and a late fetal vampire bat (Desmodus rotundus) using diceCT and µCT. Subsequently, we decalcified, serially sectioned and stained the same heads. The two CT volumes were rotated so that the sectional plane of the slice series closely matched that of histological sections, yielding the ideal opportunity to relate CT observations to corresponding histology. Olfactory epithelium is typically thicker, on average, than respiratory epithelium in both bats. Thus, one investigator (SK), blind to the histological sections, examined the diceCT slice series for both bats and annotated changes in thickness of epithelium on the first ethmoturbinal (ET I), the roof of the nasal fossa, and the nasal septum. A second trial was conducted with an added criterion: radioopacity of the lamina propria as an indicator of Bowman’s glands. Then, a second investigator (TS) annotated images of matching histological sections based on microscopic observation of epithelial type, and transferred these annotations to matching CT slices. Measurements of slices annotated according to changes in epithelial thickness alone closely track measurements of slices based on histologically-informed annotations; matching histological sections confirm blind annotations were effective based on epithelial thickness alone, except for a patch of unusually thick non-OE, mistaken for OE in one of the specimens. When characteristics of the lamina propria were added in the second trial, the blind annotations excluded the thick non-OE. Moreover, in the fetal bat the use of evidence for Bowman’s glands improved detection of olfactory mucosa, perhaps because the epithelium itself was thin enough at its margins to escape detection. We conclude that diceCT can by itself be highly effective in identifying distribution of OE, especially where observations are confirmed by histology from at least one specimen of the species. Our findings also establish that iodine staining, followed by stain removal, does not interfere with subsequent histological staining of the same specimen.

Venous networks in the upper airways of bats: A histological and diceCT study

Our knowledge of nasal cavity anatomy has grown considerably with the advent of micro-computed tomography (CT). More recently, a technique called diffusible iodine-based contrast-enhanced CT (diceCT) has rendered it possible to study nasal soft tissues. Using diceCT and histology, we aim to (a) explore the utility of these techniques for inferring the presence of venous sinuses that typify respiratory mucosa and (b) inquire whether distribution of vascular mucosa may relate to specialization for derived functions of the nasal cavity (i.e., nasal-emission of echolocation sounds) in bats. Matching histology and diceCT data indicate that diceCT can detect venous sinuses as either darkened, "empty" spaces, or radio-opaque islands when blood cells are present. Thus, we show that diceCT provides reliable information on vascular distribution in the mucosa of the nasal airways. Among the bats studied, a nonecholocating pteropodid (Cynopterus sphinx) and an oral-emitter of echolocation sounds (Eptesicus fuscus) possess venous sinus networks that drain into the sphenopalatine vein rostral to the nasopharynx. In contrast, nasopharyngeal passageways of nasal-emitting hipposiderids are notably packed with venous sinuses. The mucosae of the nasopharyngeal passageways are far less vascular in nasal-emitting phyllostomids, in which vascular mucosae are more widely distributed in the nasal cavity, and in some nectar-feeding species, a particularly large venous sinus is adjacent to the vomeronasal organ. Therefore, we do not find a common pattern of venous sinus distribution associated with nasal emission of sounds in phyllostomids and hipposiderids. Instead, vascular mucosa is more likely critical for air-conditioning and sometimes vomeronasal function in all bats.

Gross morphological and morphometric study of the upper respiratory system of the African giant rat (Cricetomys gambianus, Waterhouse 1840)

The nose is a structurally and functionally complex organ in the upper respiratory tract. It not only serves as the principal organ for the sense of smell, but also functions to efficiently filter, warm, and humidify inhaled air before the air enters the more delicate distal tracheobronchial airways and alveolar parenchyma of the lungs. Despite the volume of published studies on the biology of rodents, there is no information on the gross upper respiratory morphology of the African giant rat (AGR) in the available literature. Hence, this study aimed to examine the anatomy of the turbinates, their meatuses, and the morphometry of the nasal cavity. The following were found and reported in this study: (a) There were three nasal conchae in AGR: the nasoturbinate, which was the largest; the ethmoturbinate, which was composed of one well-developed ectoturbinate and three well-developed endoturbinates; and the maxilloturbinate, which was fusiform, short, and branched. (b) Three major meatuses were observed: the dorsal nasal meatus, which was the longest and widest; the middle nasal meatus, which was without limbs but had a deep oval caudal recess; and the ventral nasal meatus, which directly continued caudally into the nasopharyngeal meatus. (c) Four ethmoturbinates with four slit-like meatuses were observed, each with dorsal and ventral limbs; the first contacted the middle nasal meatus but not the nasopharyngeal meatus. (d) There were three paranasal sinuses: one sphenoid, two frontal, and two palatine sinuses. The data obtained are relevant to pathologists and eco-morphologists, considering the burrowing habitat and behaviors of AGR, and provide baseline data for more investigative studies.

Olfactory epithelium and ontogeny of the nasal chambers in the bowhead whale (Balaena mysticetus)

In a species of baleen whale, we identify olfactory epithelium that suggests a functional sense of smell and document the ontogeny of the surrounding olfactory anatomy. Whales must surface to breathe, thereby providing an opportunity to detect airborne odorants. Although many toothed whales (odontocetes) lack olfactory anatomy, baleen whales (mysticetes) have retained theirs. Here, we investigate fetal and postnatal specimens of bowhead whales (Balaena mysticetus). Computed tomography (CT) reveals the presence of nasal passages and nasal chambers with simple ethmoturbinates through ontogeny. Additionally, we describe the dorsal nasal meatuses and olfactory bulb chambers. The cribriform plate has foramina that communicate with the nasal chambers. We show this anatomy within the context of the whole prenatal and postnatal skull. We document the tunnel for the ethmoidal nerve (ethmoid foramen) and the rostrolateral recess of the nasal chamber, which appears postnatally. Bilateral symmetry was apparent in the postnatal nasal chambers. No such symmetry was found prenatally, possibly due to tissue deformation. No nasal air sacs were found in fetal development. Olfactory epithelium, identified histologically, covers at least part of the ethmoturbinates. We identify olfactory epithelium using six explicit criteria of mammalian olfactory epithelium. Immunohistochemistry revealed the presence of olfactory marker protein (OMP), which is only found in mature olfactory sensory neurons. Although it seems that these neurons are scarce in bowhead whales compared to typical terrestrial mammals, our results suggest that bowhead whales have a functional sense of smell, which they may use to find prey.

Domesticating olfaction: Dog breeds, including scent hounds, have reduced cribriform plate morphology relative to wolves

The domestic dog is assumed by nearly everyone to be the consummate smeller. Within the species Canis familiaris individual breeds, such as the bloodhound or beagle, are known as olfactory stars. These are "scent breeds," a grouping variably defined as a genetic clade or breed class commonly used for scent detection tasks. Previous work suggests that the dog has a more robust olfactory anatomy than many mammal species. Now we undertake a closer investigation of the dog's olfactory system, both in relationship to its closest wild relatives, the wolf and coyote, and across individual breeds. First, we seek to resolve whether the dog has lost olfactory capacity through its domestication from the wolf lineage. Second, we test the inertial lore that among dogs, "scent breeds," have a superior olfactory facility. As a measure of relative olfactory capacity, we look to the cribriform plate (CP), a bony cup in the posterior nasal cavity perforated by passageways for all olfactory nerve bundles streaming from the periphery to the brain. Using high-resolution computed tomography (CT) scans and digital quantification, we compare relative CP size in 46 dog breeds, the coyote and gray wolf. Results show the dog has a reduced CP surface area relative to the wolf and coyote. Moreover, we found no significant differences between CP size of "scent" and "non-scent" breeds. Our study suggests that the dog lost olfactory capacity as a result of domestication and this loss was not recovered in particular breed groupings through directed artificial selection for increased olfactory facility.

The dog-human connection

This special issue of The Anatomical Record is the end result of a rare convergence of researchers scattered around the globe who came together to explore the mystery of the dog-human connection. Many of the discussions at the 12th International Congress of Vertebrate Morphology in Prague (July 23, 2019) are echoed within this issue. The enigmatic origins of dog domestication (as well as feralized descendants such as the dingo) are discussed, including phases of domestication that we might infer, and our historical knowledge of dog breeding. Emphasized by the morphological and genetic data are the forces of selection, both unintentional and intentional. In our modern life with dogs, we enjoy their companionship and benefit from the utility of many breeds, but we encounter unintended health care issues that are often breed-specific. Dogs are so different in their sensory specializations (especially olfaction), but have uniquely (among other domestic mammals) developed highly sophisticated means of interspecific communication with humans. In sum, the manuscripts within this issue discuss anatomical, paleontological, genetic, and behavioral evidence bearing on the antiquity of the domestic dog, the process of domestication, and the many ways in which dogs continue to affect human life.

"Mucosal maps" of the canine nasal cavity: Micro-computed tomography and histology

Nasal turbinals, delicate and complex bones of the nasal cavity that support respiratory or olfactory mucosa (OM), are now easily studied using high resolution micro-computed tomography (μ-CT). Standard μ-CT currently lacks the capacity to identify OM or other mucosa types without additional radio-opaque staining techniques. However, even unstained mucosa is more radio-opaque than air, and thus mucosal thickness can be discerned. Here, we assess mucosal thickness of the nasal fossa using the cranium of a cadaveric adult dog that was μ-CT scanned with an isotropic resolution of 30 μm, and subsequently histologically sectioned and stained. After co-alignment of μ-CT slice planes to that of histology, mucosal thickness was estimated at four locations. Results based on either μ-CT or histology indicate olfactory mucosa is thicker on average compared with non-olfactory mucosa (non-OM). In addition, olfactory mucosa has a lesser degree of variability than the non-OM. Variability in the latter appears to relate mostly to the varying degree of vascularity of the lamina propria. Because of this, in structures with both specialized vascular respiratory mucosa and OM, such as the first ethmoturbinal (ET I), the range of thickness of OM and non-OM may overlap. Future work should assess the utility of diffusible iodine-based contrast enhanced CT techniques, which can differentiate epithelium from the lamina propria, to enhance our ability to differentiate mucosa types on more rostral ethmoturbinals. This is especially critical for structures such as ET I, which have mixed functional roles in many mammals.

Convergent evolution of olfactory and thermoregulatory capacities in small amphibious mammals

Olfaction and thermoregulation are key functions for mammals. The former is critical to feeding, mating, and predator avoidance behaviors, while the latter is essential for homeothermy. Aquatic and amphibious mammals face olfactory and thermoregulatory challenges not generally encountered by terrestrial species. In mammals, the nasal cavity houses a bony system supporting soft tissues and sensory organs implicated in either olfactory or thermoregulatory functions. It is hypothesized that to cope with aquatic environments, amphibious mammals have expanded their thermoregulatory capacity at the expense of their olfactory system. We investigated the evolutionary history of this potential trade-off using a comparative dataset of three-dimensional (3D) CT scans of 189 skulls, capturing 17 independent transitions from a strictly terrestrial to an amphibious lifestyle across small mammals (Afrosoricida, Eulipotyphla, and Rodentia). We identified rapid and repeated loss of olfactory capacities synchronously associated with gains in thermoregulatory capacity in amphibious taxa sampled from across mammalian phylogenetic diversity. Evolutionary models further reveal that these convergences result from faster rates of turbinal bone evolution and release of selective constraints on the thermoregulatory-olfaction trade-off in amphibious species. Lastly, we demonstrated that traits related to vital functions evolved faster to the optimum compared to traits that are not related to vital functions.

Biomechanical simulations reveal a trade-off between adaptation to glacial climate and dietary niche versatility in European cave bears

The cave bear is one of the best known extinct large mammals that inhabited Europe during the "Ice Age," becoming extinct ≈24,000 years ago along with other members of the Pleistocene megafauna. Long-standing hypotheses speculate that many cave bears died during their long hibernation periods, which were necessary to overcome the severe and prolonged winters of the Last Glacial. Here, we investigate how long hibernation periods in cave bears would have directly affected their feeding biomechanics using CT-based biomechanical simulations of skulls of cave and extant bears. Our results demonstrate that although large paranasal sinuses were necessary for, and consistent with, long hibernation periods, trade-offs in sinus-associated cranial biomechanical traits restricted cave bears to feed exclusively on low energetic vegetal resources during the predormancy period. This biomechanical trade-off constitutes a new key factor to mechanistically explain the demise of this dominant Pleistocene megafaunal species as a direct consequence of climate cooling.

Nasal airflow in the pygmy slow loris (Nycticebus pygmaeus) based on a combined histological, computed tomographic and computational fluid dynamics methodology

'Macrosmatic' mammals have dedicated olfactory regions within their nasal cavity and segregated airstreams for olfaction and respiratory air-conditioning. Here, we examined the 3D distribution of olfactory surface area (SA) and nasal airflow patterns in the pygmy slow loris (Nycticebus pygmaeus), a primate with primitive nasal cavities, except for enlarged eyes that converge upon the posterodorsal nasal region. Using the head of an adult loris cadaver, we co-registered micro-computed tomography (CT) slices and histology sections to create a 3D reconstruction of the olfactory mucosa distribution. Histological sections were used to measure olfactory surface area and to annotate CT reconstructions. The loris has a complex olfactory recess (∼19% of total nasal SA) with multiple olfactory turbinals. However, the first ethmoturbinal has a rostral projection that extends far anterior to the olfactory recess, lined by ∼90% non-olfactory epithelium. Only one (of three) frontoturbinals bears olfactory mucosa. Computational fluid dynamics simulations of nasal airflow and odorant deposition revealed that there is some segregation of respiratory and olfactory flow in the loris nose, but that it is not as distinct as in well-studied 'macrosmats' (e.g. the dog). In the loris, airflow is segregated medially and laterally to vertically elongated, plate-like first ethmoturbinals. Thus, lorises may be said to have certain macrosmatic anatomical characteristics (e.g. olfactory recess), but not segregated nasal airflow patterns that are optimized for olfaction, as in canids. These results imply that a binary 'microsmatic/macrosmatic' dichotomy does not exist. Rather, mammals appear to exhibit complex trends with respect to specialization of the turbinals and recesses.

Internal nasal morphology of the Eocene primate Rooneyia viejaensis and extant Euarchonta: Using μCT scan data to understand and infer patterns of nasal fossa evolution in primates

Primates have historically been viewed as having a diminished sense of smell compared to other mammals. In haplorhines, olfactory reduction has been inferred partly based on the complexity of the bony turbinals within the nasal cavity. Some turbinals are covered in olfactory epithelium, which contains olfactory receptor neurons that detect odorants. Accordingly, turbinal number and complexity has been used as a rough anatomical proxy for the relative importance of olfactory cues for an animal's behavioral ecology. Unfortunately, turbinals are delicate and rarely preserved in fossil specimens, limiting opportunities to make direct observations of the olfactory periphery in extinct primates. Here we describe the turbinal morphology of Rooneyia viejaensis, a late middle Eocene primate of uncertain phylogenetic affinities from the Tornillo Basin of West Texas. This species is currently the oldest fossil primate for which turbinals are preserved with minimal damage or distortion. Microcomputed tomography (μCT) reveals that Rooneyia possessed 1 nasoturbinal, 4 bullar ethmoturbinals, 1 frontoturbinal, 1 interturbinal, and an olfactory recess. This pattern is broadly similar to the condition seen in some extant strepsirrhine primates but differs substantially from the condition seen in extant haplorhines. Crown haplorhines possess only two ethmoturbinals and lack frontoturbinals, interturbinals, and an olfactory recess. Additionally, crown anthropoids have ethmoturbinals that are non-bullar. These observations reinforce the conclusion that Rooneyia is not a stem tarsiiform or stem anthropoid. However, estimated olfactory turbinal surface area in Rooneyia is greater than that of similar-sized haplorhines but smaller than that of similar-sized lemuriforms and lorisiforms. This finding suggests that although Rooneyia was broadly plesiomorphic in retaining a large complement of olfactory turbinals as in living strepsirrhines, Rooneyia may have evolved somewhat diminished olfactory abilities as in living haplorhines.

Convergent evolution of an extreme dietary specialisation, the olfactory system of worm-eating rodents

Turbinal bones are key components of the mammalian rostrum that contribute to three critical functions: (1) homeothermy, (2) water conservation and (3) olfaction. With over 700 extant species, murine rodents (Murinae) are the most species-rich mammalian subfamily, with most of that diversity residing in the Indo-Australian Archipelago. Their evolutionary history includes several cases of putative, but untested ecomorphological convergence, especially with traits related to diet. Among the most spectacular rodent ecomorphs are the vermivores which independently evolved in several island systems. We used 3D CT-scans (N = 87) of murine turbinal bones to quantify olfactory capacities as well as heat or water conservation adaptations. We obtained similar results from an existing 2D complexity method and two new 3D methodologies that quantify bone complexity. Using comparative phylogenetic methods, we identified a significant convergent signal in the rostral morphology within the highly specialised vermivores. Vermivorous species have significantly larger and more complex olfactory turbinals than do carnivores and omnivores. Increased olfactory capacities may be a major adaptive feature facilitating rats' capacity to prey on elusive earthworms. The narrow snout that characterises vermivores exhibits significantly reduced respiratory turbinals, which may reduce their heat and water conservation capacities.

The Influence of Sniffing on Airflow and Odorant Deposition in the Canine Nasal Cavity

Nasal airflow plays a critical role in olfaction by transporting odorant from the environment to the olfactory epithelium, where chemical detection occurs. Most studies of olfaction neglect the unsteadiness of sniffing and assume that nasal airflow and odorant transport are "quasi-steady," wherein reality most mammals "sniff." Here, we perform computational fluid dynamics simulations of airflow and odorant deposition in an anatomically accurate model of the coyote (Canis latrans) nasal cavity during quiet breathing, a notional quasi-steady sniff, and unsteady sniffing to: quantify the influence of unsteady sniffing, assess the validity of the quasi-steady assumption, and investigate the functional advantages of sniffing compared to breathing. Our results reveal that flow unsteadiness during sniffing does not appreciably influence qualitative (gross airflow and odorant deposition patterns) or quantitative (time-averaged olfactory flow rate and odorant uptake) measures of olfactory function. A quasi-steady approximation is, therefore, justified for simulating time-averaged olfactory function in the canine nose. Simulations of sniffing versus quiet breathing demonstrate that sniffing delivers about 2.5 times more air to the olfactory recess and results in 2.5-3 times more uptake of highly- and moderately-soluble odorants in the sensory region per unit time, suggesting one reason why dogs actively sniff. Simulations also reveal significantly different deposition patterns in the olfactory region during inspiration for different odorants, and that during expiration there is little retronasal odorant deposition in the sensory region. These results significantly improve our understanding of canine olfaction, and have several practical implications regarding computer simulation of olfactory function.

Unique Turbinal Morphology in Horseshoe Bats (Chiroptera: Rhinolophidae)

The mammalian nasal fossa contains a set of delicate and often structurally complex bones called turbinals. Turbinals and associated mucosae function in regulating respiratory heat and water loss, increasing surface area for olfactory tissue, and directing airflow within the nasal fossa. We used high-resolution micro-CT scanning to investigate a unique maxilloturbinal morphology in 37 species from the bat family Rhinolophidae, which we compared with those of families Hipposideridae, Megadermatidae, and Pteropodidae. Rhinolophids exhibit numerous structural modifications along the nasopharyngeal tract associated with emission of high duty cycle echolocation calls via the nostrils. In rhinolophids, we found that the maxilloturbinals and a portion of ethmoturbinal I form a pair of strand-like bony structures on each side of the nasal chamber. These structures project anteriorly from the transverse lamina and complete a hairpin turn to project posteriorly down the nasopharyngeal duct, and vary in length among species. The strand-like maxilloturbinals in Rhinolophidae were not observed in our outgroups and represent a synapomorphy for this family, and are unique in form among mammals. Within Rhinolophidae, maxilloturbinal size and cross-sectional shape were correlated with phylogeny. We hypothesize that strand-shaped maxilloturbinals may function to reduce respiratory heat and water loss without greatly impacting echolocation call transmission since they provide increased mucosal surface area for heat and moisture exchange but occupy minimal space. Alternatively, they may play a role in transmission of echolocation calls since they are located directly along the path sound travels between the larynx and nostrils during call emission. Anat Rec, 300:309-325, 2017. © 2016 Wiley Periodicals, Inc.

The influence of nasal airflow on respiratory and olfactory epithelial distribution in felids

The surface area of the maxilloturbinals and fronto-ethmoturbinals is commonly used as an osteological proxy for the respiratory and the olfactory epithelium, respectively. However, this assumption does not fully account for animals with short snouts in which these two turbinal structures significantly overlap, potentially placing fronto-ethmoturbinals in the path of respiratory airflow. In these species, it is possible that anterior fronto-ethmoturbinals are covered with non-sensory (respiratory) epithelium instead of olfactory epithelium. In this study, we analyzed the distribution of olfactory and non-sensory, respiratory epithelia on the turbinals of two domestic cats (Felis catus) and a bobcat (Lynx rufus). We also conducted a computational fluid dynamics simulation of nasal airflow in the bobcat to explore the relationship between epithelial distribution and airflow patterns. The results showed that a substantial amount of respiratory airflow passes over the anterior fronto-ethmoturbinals, and that contrary to what has been observed in caniform carnivorans, much of the anterior ethmoturbinals are covered by non-sensory epithelium. This confirms that in short-snouted felids, portions of the fronto-ethmoturbinals have been recruited for respiration, and that estimates of olfactory epithelial coverage based purely on fronto-ethmoturbinal surface area will be exaggerated. The correlation between the shape of the anterior fronto-ethmoturbinals and the direction of respiratory airflow suggests that in short-snouted species, CT data alone are useful in assessing airflow patterns and epithelium distribution on the turbinals.