Abnormal Nasal Passage Morphology in an Adult Gharial (Gavialis gangeticus) Implications for Airflow and Nasal Septum Development in Longirostrine Crocodylians

Abstract

Gharials are unique among extant crocodylians for their extremely longirostrine skull morphology. The extensively elongate rostrum in this group is comprised of contributions from the premaxillae, maxillae, palatines, vomers and pterygoids. Unlike some brevirostrine crocodylian taxa, the vomers do not support the nasal septum throughout its course, but terminate approximately 1 cm distal to the prefrontal‐maxillary suture. Nasal septum integrity is maintained via a septal sulcus produced by the sharp ventral dip along the midline of the two maxillae as they join together to form the floor of the nasal cavity. In other longirostrine crocodylians such as Alligator and Crocodylus, this septal sulcus is pronounced and holds the septum in place for most of the nasal passage. However, in Gavialis the septal sulcus is weakly developed and the septum largely rests on the suture‐line of the maxillae instead. Here we describe a unique case of a large adult female gharial with an extensively deviated septum. Deviation of the nasal septum produced a strong sigmoidal shape to the nasal passage rostral to the orbit. Segmentations and 3D renderings made in Avizo 7.1 (Thermo Fisher Scientific) and Computational Fluid Dynamic analysis using ANSYS Fluent (ANSYS Inc.) were run on this deviated airway to better determine the effects this wavy septum had on airflow. Results revealed a slightly elevated resistance in nasal airflow with the production of a few, small vortices within the bends of the nasal passage. These secondary flow patterns were not enough to induce turbulent flow and the majority of the nasal passage maintained laminar flow pattern similar to other crocodylians. Our results suggest that in spite of the heavily deviated septum, this animal was able to breathe with little extra effort. We compared this specimen to two other Gavialis specimens and discovered similar, albeit weaker developed, deviations of the nasal septum in these specimens as well. We suspect that weak development of the septal sulcus in Gavialis leaves this species susceptible to septal deviations and this type of developmental abnormality may be fairly common for this species and potentially other species of crocodylians with extensively elongated rostra.