Nasal turbinals and laminae homologies in pangolins: insights from developments

Abstract The mammalian nasal cavity houses complex turbinals and laminae that conserve heat and moisture and mediate olfaction. Despite renewed interest driven by CT technology, some mammals remain scarcely studied, especially from developmental perspectives. This is true for pangolins, hypothesized to possess unique turbinals due to their elongated rostrum and possible olfactory adaptations for a specialized diet. Their turbinal complexity makes it difficult to establish hypotheses of homology with other mammals. Foetal anatomy and ontogenetic changes in the nasal capsule, therefore, provide key insights for assessing turbinal homology. Using diceCT, we reconstructed the foetal nasal capsules of Manis pentadactyla and M. javanica, and examined adults representing seven pangolin species, to clarify homology. By mapping turbinal and lamina traits on to a molecular phylogeny, we propose an evolutionary scenario for the morphology. Maxilloturbinals differ between Asian pangolins (double-scrolled folds) and African pangolins (a double scroll with a small caudal branch). Ethmoturbinal complexity also varies: in all pangolins, ethmoturbinal I comprises rostral (pars anterior) and caudal (pars posterior) portions, with lineage-specific degrees of subsequent fusion. These observations support two possible evolutionary pathways for the ethmoturbinal I: (i) complete separation into distinct pars; (ii) initial separation followed by secondary fusion in some lineages.