For nasal obstruction, options can be septoplasty, turbinate reductions, or surgical palate expansion. A turbinectomy is mainly performed for turbinate hypertrophy, when the turbinates are swollen and enlarged. Nonallergic rhinitis cases may subsequently develop polyps, turbinate hypertrophy and sinusitis. Septoplasty and turbinate surgery may improve the nasal airway. Mucus is a normal protective layering around the airway, eye, nasal turbinate, and urogenital tract. Often the inferior turbinate on the opposite side enlarges, which is termed "compensatory hypertrophy". Treatment of the underlying allergy or irritant may reduce turbinate swelling. Furthermore, ossified turbinate bones have been identified in the ankylosaurid dinosaur "Saichania". Bullosa refers to the air-filled cavity within the turbinate. The form of the shell varies from discoidal to turbinate. The shape may also be subglobose, turbinate or helicoid. Males differ from females in having turbinate eyes. They have a depressed or turbinate shape. Stromata of some species (Podostroma) are clavate or turbinate. This same complex turbinate structure helps conserve water in arid environments.