Structure and function of respiratory turbinates in phocid seals

Matthew J Mason,Arnoldus S Blix,Léa M D Wenger,Øyvind Hammer

doi:10.1007/s00300-019-02618-w

Matthew J Mason, Arnoldus S Blix + Show 2 more

Open Access

https://doi.org/10.1007/s00300-019-02618-w

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Abstract

In terrestrial mammals, the respiratory turbinate bones within the nasal cavity are employed to conserve heat and water. In order to investigate whether environmental temperature affects respiratory turbinate structure in phocids, we used micro-computed tomography to compare maxilloturbinate bone morphology in polar seals, grey seals and monk seals. The maxilloturbinates of polar seals have much higher surface areas than those of monk seals, the result of the polar seals having more densely packed, complex turbinates within larger nasal cavities. Grey seals were intermediate; a juvenile of this species proved to have more densely packed maxilloturbinates with shorter branch lengths than a conspecific adult. Fractal dimension in the densest part of the maxilloturbinate mass was very close to 2 in all seals, indicating that these convoluted bones evenly fill the available space. The much more elaborate maxilloturbinate systems in polar seals, compared with monk seals, are consistent with a greater need to limit respiratory heat loss.

Highlights

Described as “one of the most distinctive of mammalian features” (Hillenius 1992), the turbinate bones are thin, scrolllike or branched bony plates which partially fill the nasal cavity (Negus 1958; Moore 1981; Hillenius 1992)
The methods used here to process the CT data clearly involved an element of subjectivity, but were chosen because the resulting black-and-white images were much better representations of turbinate structure than anything that we could achieve in an automated way, when compared with the original, greyscale tomograms
Manual editing and segmentation has been used in comparable studies of turbinate structure, when considering poorly resolved regions (Craven et al 2007; Xi et al 2016)

Summary

Introduction

Described as “one of the most distinctive of mammalian features” (Hillenius 1992), the turbinate bones are thin, scrolllike or branched bony plates which partially fill the nasal cavity (Negus 1958; Moore 1981; Hillenius 1992). Domestic cat nasoturbinates are at least partially covered in olfactory epithelium (Van Valkenburgh et al 2014a), but the main role of nasoturbinates in carnivores may be to help direct airflow to the olfactory region in the posterior part of the nasal cavity (Van Valkenburgh et al 2014b) In this olfactory region, blind recesses are formed between complex turbinates covered in olfactory epithelium. Ethmoturbinates, frontoturbinates and interturbinates have been described in domestic dogs, but their precise identification is difficult without recourse to an ontogenetic series, and nomenclature has varied in different studies (Wagner and Ruf 2019) These bones will be referred to collectively as ‘olfactory turbinates’ (Fig. 1), the anterior part of the first ethmoturbinate was found to be covered in respiratory epithelium in Felis and Lynx (Van Valkenburgh et al 2014a)

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