The aerodynamic filtering system of the sandfish lizard

The sandfish lizard Scincus scincus spends almost its entire life buried in aeolian sand. To prevent sand grains from entering its lungs, it was hypothesized [1] that particles are aerodynamically filtered when they enter the nasal cavity: The vestibulum is a narrow rounded channel leading to a kind of „chamber“, where cilia and mucus are present. In this chamber the particles get caught by mucus during a slow, long-lasting inhalation (2 s), and eventually get exhaled because of an intense, cough-like exhalation that lasts only 45 ms. To verify this theory we studied the filtering system by computational fluid dynamics simulations of fluid and particle flow. The results show that during inhalation the flow profile anterior to and in the chamber is characterized by strong cross-flow velocities that move the sand grains towards the mucus-covered wall; during the intense exhalation particles of all sizes are coughed out. In this context we explore the possibility to optimize state-of-the-art filtering systems.