Scaling of the first ethmoturbinal in nocturnal strepsirrhines: Olfactory and respiratory surfaces

Abstract

Turbinals (scroll bones, turbinates) are projections from the lateral wall of the nasal fossa. These bones vary from simple folds to branching scrolls. Conventionally, maxilloturbinals comprise the respiratory turbinals, whereas nasoturbinals and ethmoturbinals comprise olfactory turbinals, denoting the primary type of mucosa that lines these conchae. However, the first ethmoturbinal (ETI) appears exceptional in the variability of it mucosal covering. Recently, it was suggested that the distribution of respiratory versus olfactory mucosae varies based on body size or age in strepsirrhine primates (lemurs and lorises). The present study was undertaken to determine how the rostrocaudal distribution of olfactory epithelium (OE) versus non-OE scales relative to palatal length in strepsirrhines. Serially sectioned heads of 20 strepsirrhines (10 neonates, 10 adults) were examined for presence of OE on ETI, rostral to its attachment to the nasal fossa wall (lateral root). Based on known distances between sections of ETI, the rostrocaudal length of OE was measured and compared to the length lined solely by non-OE (primarily respiratory epithelium). In 13 specimens, the total surface area of OE versus non-OE was calculated. Results show that the length of non-OE scales nearly isometrically with cranial length, while OE is more negatively allometric. In surface area, a lesser percentage of non-OE exists in smaller species than larger species and between neonates and adults. Such results are consistent with recent suggestions that the olfactory structures do not scale closely with body size, whereas respiratory structures (e.g., maxilloturbinals) may scale close to isometry. In primates and perhaps other mammals, variation in ETI morphology may reflect dual adaptations for olfaction and endothermy. Anat Rec, 290:215-237, 2007. 2007 Wiley-Liss, Inc.

Nasal Fossa of Mouse and Dwarf Lemurs (Primates, Cheirogaleidae)

“…A small patch of olfactory epithelium extends into the apex of the anterolateral recess, just anterior to the beginning of the frontal recess. The proportionally extensive anterior distribution of respiratory mucosa on ethmoturbinal I was previously described in cheirogaleids (Smith et al, 2007b). The adjacent maxilloturbinal is only partly ciliated.…”

“…10). Whereas this study did not quantify respiratory mucosa, the preponderance of respiratory mucosa on nonolfactory parts of ethmoturbinal I (Smith et al, 2007b) and the mucosa of the maxilloturbinal (see below) suggests that the growth in these anterior regions augments air-conditioning capacity.…”

“…Turbinals of the ethmoid bone and adjacent surfaces of the midline septum bear olfactory epithelium in all mammals described to date. However, descriptions of diverse taxa (ungulates, carnivores, bats, insectivores, primates, and marsupials) indicate that some ethmoidal turbinals are partially covered by respiratory mucosa (Read, 1908;Negus, 1958;Loo, 1974;Bhatnagar and Kallen, 1975;Kumar et al, 1993Kumar et al, , 2000Rowe et al, 2005;Smith et al, 2007b). This variation in the mucosal distribution along ethmoidal turbinals and adjacent structures requires more detailed investigation (Smith et al, 2007a,b).…”

Distribution of Olfactory and Nonolfactory Surface Area in the Nasal Fossa of Microcebus murinus: Implications for Microcomputed Tomography and Airflow Studies

“…By each estimate, the maxilloturbinal comprises approximately one-fifth of total nasal fossa SA. Also, in terms of the division of labor vis-à-vis olfactory and respiratory function, both studies attribute dual function to the first ET (see also Smith et al, 2007a). However, Rowe et al assign all ETs (using the term ''endoturbinals'') caudal to ET I to solely an olfactory function, whereas this study indicates only closer to one-half of the SA of the posterior ETs is covered with olfactory neuroepithelium.…”

“…The mucosal distribution in Monodelphis was estimated based on a comparison of adult CT slices to histology from subadults. If Monodelphis has a disproportionate age-related increase in nonolfactory mucosa, as observed for primates (Smith et al, 2007a), the mucosal estimates for the ETs may somewhat overestimate the amount of olfactory mucosa.…”