This secreted mucus covers the nasal cavities, and serves as a filter, by trapping air-borne particles larger than 2 to 3 micrometers. The respiratory epithelium also serves as a means of access for the lymphatic system, which protects the body from being infected by viruses or bacteria. Smell
The conchae provide, first and foremost, the humidity needed to preserve the delicate olfactory epithelium, which in turn is needed to keep the olfactory receptors healthy and alert. If the epithelial layer gets dry or irritated, it may cease to function. This is usually a temporary condition but, over time, may lead to chronic anosmia. The turbinates also increase the surface area of the inside of the nose, and, by directing and deflecting airflow across the maximum mucosal surface of the inner nose, they are able to propel the inspired air. This, coupled with the humidity and filtration provided by the conchae, helps to carry more scent molecules towards the higher, and very narrow regions of the nasal airways, where olfaction nerve receptors are located.The superior conchae completely cover and protect the nerve axons piercing through the cribriform plate (a porous bone plate that separates the nose from the brain) into the nose. Some areas of the middle conchae are also innervated by the olfactory bulb. All three pairs of conchae are innervated by pain and temperature receptors, via the trigeminal nerve (or, the fifth cranial nerve).
While the maxilloturbinates of mammals are located in the path of airflow to collect moisture, sensory turbinates in both mammals and reptiles are positioned farther back and above the nasal passage, away from the flow of air. Glanosuchus has ridges positioned low in the nasal cavity, indicating that it had maxilloturbinates that were in the direct path of airflow. The maxilloturbinates may not have been preserved because they were either very thin or cartilaginous. The possibility has also been raised that these ridges are associated with an olfactory epithelium rather than turbinates. Nonetheless, the possible presence of maxilloturbinates suggests that Glanosuchus may have been able to rapidly breathe without drying out the nasal passage, and therefore could have been an endotherm.The bones of nasal turbinates are very fragile and seldom survive as fossils. In particular none have been found in fossil birds. But there is indirect evidence for their presence in some fossils. Rudimentary ridges like those that support respiratory turbinates have been found in advanced Triassic cynodonts, such as Thrinaxodon and Diademodon. This suggests that they may have had fairly high metabolic rates. The paleontologist John Ruben and others have argued that no evidence of nasal turbinates has been found in dinosaurs. All the dinosaurs they examined had nasal passages that they claimed were too narrow and too short to accommodate nasal turbinates, so dinosaurs could not have sustained the breathing rate required for a mammal-like or bird-like metabolic rate while at rest, because their lungs would have dried out.