Nasal morphometry in marmosets: loss and redistribution of olfactory surface area.

The two major groups of primates differ in internal nasal anatomy. Strepsirrhines (e.g., lemurs) have more numerous turbinals and recesses compared with haplorhines (e.g., monkeys). Since detailed quantitative comparisons of nasal surface area (SA) have not been made, we measured mucosa in serially sectioned monkeys (Callithrix jacchus, Cebuella pygmaea). Data were compared with previously published findings on the mouse lemur, Microcebus murinus. The nasal airways were digitally reconstructed using computed tomography scanned heads of Cebuella and Microcebus. In addition, morphometric and functional analyses were carried out using segmented photographs of the histological sections of Cebuella and Microcebus. The SA of the ethmoturbinal complex is about half as large in marmosets compared with Microcebus, and is covered with less olfactory mucosa (18%-24% in marmosets, compared with ∼ 50% in Microcebus). Whereas the ethmoturbinal complex of Microcebus bears half of the total olfactory mucosa in the nasal airway, most (∼ 80%) olfactory mucosa is distributed on other surfaces in the marmosets (e.g., nasal septum). A comparison to previously published data suggests all primate species have less olfactory surface area (OSA) compared with other similar-sized mammals, but this is especially true of marmosets. Taken together, these findings support the hypothesis that there is a reduced OSA in at least some haplorhines, and this can be linked to diminished posterosuperior dimensions of the nasal fossae. However, haplorhines may have minimized their olfactory loss by redistributing olfactory mucosa on non-turbinal surfaces. Our findings also imply that airflow patterns in the olfactory region differ among primates.