Septal deviation in the nose of the longest faced crocodylian: A description of nasal anatomy and airflow in the Indian gharial (Gavialis gangeticus) with comments on acoustics

Abstract

The remarkably thin rostrum in the Indian gharial (Gavialis gangeticus) imparts challenges to nasal physiology. Competition for space in the slim jaws necessitates a thin nasal septum, leaving this taxon susceptible to nasal passage abnormalities such as septal deviation. Here we describe the nasal anatomy of gharials based on multiple individuals including one that showcases an extreme instance of nasal septum deviation. We found that gharials have both confluent nostrils and choanae, which may be important for their unique nasal acoustics. The deviated nasal septum in the female showed distinct waviness that affected the nasal passages by alternately compressing them. We performed a computational fluid dynamic analysis on the nasal passages to visualize the effects of septal deviation on airflow. Our analysis found the deviated septum increased nasal resistance and wall shear stress during respiration, resulting in unequal distribution of the air field between both sides of the nasal passage. Our findings indicate that gharials-and potentially other longirostrine crocodylians-may be particularly susceptible to septal deviations. Lastly, we observed pterygoid bullae to be present in both sexes, though their morphology differed. Airflow in the male pterygoid bullae produced a Bernoulli effect which may be responsible for the unique "pop" sounds recorded in this species.

Soft tissues influence nasal airflow in diapsids: Implications for dinosaurs

“…As such, the patterns we observed in the yearling should largely reflect patterns seen in the adult animal. We find support for our interpretation in a recent study on nasal airflow in gharials (Bourke et al, 2022). Both crocodylians share a similar nasal passage arrangement complete with an olfactory recess.…”

“…At this size, our models should have the necessary number of nodes and cells to capture the details of resting airflow patterns that we were looking for in our study. For more complicated analyses of heat transfer or wall shear stress (e.g., Bourke et al, 2018Bourke et al, , 2022, hexahedral, polyhedral, or hybrid meshes would be a better choice for capturing the subtle interactions at the fluid-wall boundary.…”

“…All of these studies relied on inferences of nasal airflow based on anatomy, behavioral analyses, and basic fluid dynamics (e.g., Bang, 1971; Schwenk, 1993). More recent work has examined specific aspects of diapsid nasal passages in relation to nasal geometry and airflow (Bourke & Witmer, 2016; Bourke et al, 2022). However, a broader comparative survey of airflow dynamics in diapsids has yet to be performed.…”

Dispatches from the age of crocodiles: New discoveries from ancient lineages

“…In addition to comparing approaches in imaging large and small specimens of extant species, they present a series of examples of imaging and modeling jaw muscle anatomy and 3D muscle architecture. Bourke et al (2022) use imaging and computational flow dynamics to model how the nasal passages and pterygoid bullae are ventilated in a sample of gharials and other longirostrine taxa. They found that a deviated nasal septum negatively impacts air resistance.…”

Teeth to the right of me, teeth to the left of me, teeth in front of me –hello to the world of crocodiles and their many relatives in a new special issue of The Anatomical Record

“…He has become one of the leading comparative reptilian anatomists/paleo‐anatomists in the world today and has published extensively. Casey's science has often graced our pages covering, for example: new cephalic vascular anatomy in flamingos (Holliday, Ridgely, Balanoff, & Witmer, 2006); new insights into dinosaur jaw anatomy (Holliday, 2009); study of trigeminal nerve morphology in alligators with implications for understanding crocodyliform facial sensation and evolution (George & Holliday, 2013); studies on the frontoparietal fossa and dorsotemporal fenestra of archosaurs for interpreting anatomy in dinosaurs (Holliday, Porter, Vliet, & Witmer, 2020); explorations of the nose of gharials to understand airflow and acoustics (Bourke, Fontenot, & Holliday, 2022, this volume); new approaches in imaging to understand anatomy and mechanics of crocodilian jaw muscles (Holliday et al, 2022, this volume); biomechanical assessment of the craniomandibular complex of the notosuchian, Araripesuchus gomesii (Nieto, Degrange, Sellers, Diogo, & Holliday, 2022, this volume); and the effects of skull flattening on suchian jaw muscle evolution (Sellers et al, 2022, this volume). Thanks to both Casey and Emma (Figure 1a, b) for sharing their best science so often in our journal!…”