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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.

The domestic dog is assumed by nearly everyone to be the consummate smeller. Within the speciesCanis familiarisindividual 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.

It is widely accepted that obligate aquatic mammals, specifically toothed whales, rely relatively little on olfaction. There is less agreement about the importance of smell among aquatic mammals with residual ties to land, such as pinnipeds and sea otters. Field observations of marine carnivorans stress their keen use of smell while on land or pack ice. Yet, one dimension of olfactory ecology is often overlooked: while underwater, aquatic carnivorans forage “noseblind,” diving with nares closed, removed from airborne chemical cues. For this reason, we predicted marine carnivorans would have reduced olfactory anatomy relative to closely related terrestrial carnivorans. Moreover, because species that dive deeper and longer forage farther removed from surface scent cues, we predicted further reductions in their olfactory anatomy. To test these hypotheses, we looked to the cribriform plate (CP), a perforated bone in the posterior nasal chamber of mammals that serves as the only passageway for olfactory nerves crossing from the periphery to the olfactory bulb and thus covaries in size with relative olfactory innervation. Using CT scans and digital quantification, we compared CP morphology across Arctoidea, a clade at the interface of terrestrial and aquatic ecologies. We found that aquatic carnivoran species from two lineages that independently reinvaded marine environments (Pinnipedia and Mustelidae), have significantly reduced relative CP than terrestrial species. Furthermore, within these aquatic lineages, diving depth and duration were strongly correlated with CP loss, and the most extreme divers, elephant seals, displayed the greatest reductions. These observations suggest that CP reduction in carnivorans is an adaptive response to shifting selection pressures during secondary invasion of marine environments, particularly to foraging at great depths. Because the CP is fairly well preserved in the fossil record, using methods presented here to quantify CP morphology in extinct species could further clarify evolutionary patterns of olfactory loss across aquatic mammal lineages that have independently committed to life in water.

Dog owners are often impressed by their dog's sense of smell. Many of these dogs, however, have skulls that are quite altered from those of their closest canid relatives. Housed within these skulls are essential olfactory structures like the cribriform plate that play a role in olfaction and the transmission of olfactory nerve impulses to the olfactory bulb of the brain. With improvements in CT technology and accessibility, we are now able to digitally reconstruct in 3D cribriform plate morphology and study its variation within and among species. In this study, we CT scanned the skulls of 95 dog specimens from 45 different domestic dog breeds and 12 species of wild canid and compared the shape of the cribriform plate among three main groups: domestic dog breeds, wolf‐like canids, and fox‐like canids. Despite only recent selective pressure for extreme skull morphology, domestic dogs display much more variation in cribriform plate shape than wild canids, indicating that cribriform plate shape is plastic and linked to skull shape. Intense artificial selection on domestic dog skull phenotype in the last 200 years has clear effects on secondary features of the domestic dog skull, implying that selection for overt phenotypes also can impact other anatomical features associated with the skull, like the cribriform plate.