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Abstract Comparative studies rely on the identification of homologous traits, which is challenging especially when adult stages alone are available. Inferring homology from developmental series represents the most reliable approach to recognize similar phenotypes. The primate nasal cavity exhibits a plastic morphology (shape) and topology (structure) which challenge the terminology of turbinals. Turbinal development largely corresponds to the therian template: turbinals emerge from the cartilaginous nasal capsule, ossify endochondrally, and increase their size through appositional bone growth. We studied histological serial sections and µCT data of eleven primate species in six genera representing four to five age stages (fetal to adult), and the neonate and adult stage of another primate species. We reconstructed cartilaginous precursors and followed their growth patterns until adulthood to inform the identification of structures. The developmental stages were transformed to character states for better comparison across the sample. Strepsirrhines conserved the plesiomorphic condition, with turbinal morphology similar to other placentals. In contrast, haplorhines showed a reduced turbinal number. Most strikingly, some cartilaginous turbinals are absent in the ossified nasal cavity (Saguinus); others seem to emerge as appositional bone without a cartilaginous precursor (Aotus,Pithecia). Our observation that successive developmental sequences differ from the established placental template emphasizes the significance of ontogenetic series for comparative anatomy. Structures which exhibit analogous growth patterns might be falsely considered as being homologous in adults, resulting in biased phenotypic data that strongly affects comparative analyses (e.g., phylogenetic reconstructions). 

Abstract Nasal anatomy in rodents is well-studied, but most current knowledge is based on small-bodied muroid species. Nasal anatomy and histology of hystricognaths, the largest living rodents, remains poorly understood. Here, we describe the nasal cavity of agoutis ( Dasyprocta spp.), the first large-bodied South American rodents to be studied histologically throughout the nasal cavity. Two adult agoutis were studied using microcomputed tomography, and in one of these, half the snout was serially sectioned and stained for microscopic study. Certain features are notable in Dasyprocta . The frontal recess has five turbinals within it, the most in this space compared to other rodents that have been studied. The nasoturbinal is particularly large in dorsoventral and rostrocaudal dimensions and is entirely non-olfactory in function, in apparent contrast to known muroids. Whether this relates solely to body size scaling or perhaps also relates to directing airflow or conditioning inspired air requires further study. In addition, olfactory epithelium appears more restricted to the olfactory and frontal recesses compared to muroids. At the same time, the rostral tips of the olfactory turbinals bear at least some non-olfactory epithelium. The findings of this study support the hypothesis that turbinals are multifunctional structures, indicating investigators should use caution when categorizing turbinals as specialized for one function (e.g., olfaction or respiratory air-conditioning). Caution may be especially appropriate in the case of large-bodied mammals, in which the different scaling characteristics of respiratory and olfactory mucosa result in relative more of the former type as body size increases.