Primate Diversity of the Nasal Conchae: Are there Functional Differences?

Abstract

Despite their great importance in normal respiration, the nasal conchae have undergone a substantial amount of evolutionary change among the primates. With strepsirhines retaining a primitive condition of four to six ethmoturbinals situated in a committed recessus olfactorius, haplorhines have departed from this condition by expressing only one or two ethmoturbinals and lacking a transverse ethmoidal lamina that would otherwise separate respiratory and olfactory areas of the nose. Among the most derived of the haplorhines are humans, who have undergone a substantial restructuring of the facial skeleton and upper airway over the evolution of the genus Homo. Yet, even among humans, there is an impressive array of variation that may, at times, become of clinical importance. We assessed variability in the number of conchae among 16 human cadavers (nine females and seven males). It was found that all possessed a total of three nasal conchae but a great amount of diversity in the size and appearance of the ethmoturbinals was present. We found two cases of a bifid first ethmoturbinal, one case of concha bullosa, and one case of an extremely small second ethmoturbinal. The results indicate that, among humans, the inferior turbinate is far less variable in morphology than the ethmoturbinals. This is likely related to its role as the primary center for heat and moisture exchange during normal respiration. We posit that this is a functionally constrained structure that cannot accommodate as much morphological variation as the ethmoturbinals, which lie further from the areas of highest airflow velocity.