through
nares (nostrils) which expand during exercise. The nasal passages have two turbinates on either side which increase the surface area to which air is exposed. Generally, in animals, nasal conchae are convoluted structures of thin bone or cartilage located in the
nasal cavity. These are lined with
mucous membranes that can perform two functions. They can improve the sense of smell by increasing the area available to absorb airborne chemicals, and they can warm and moisten inhaled air, and extract heat and moisture from exhaled air to prevent
desiccation of the lungs.
Olfactory turbinates are found in all living
tetrapods, and
respiratory turbinates are found in most mammals and birds. Animals with respiratory turbinates can breathe faster without drying out their lungs, and consequently can have a faster metabolism.
Dogs and other
canids possess well-developed nasal turbinates. These turbinates allow for heat exchange between small arteries and veins on their
maxilloturbinate (turbinates positioned on
maxilla bone) surfaces in a counter-current heat-exchange system. The water conservation and thermoregulatory capabilities of these well-developed turbinates in dogs may have been crucial adaptations that allowed dogs (including both domestic dogs and their wild prehistoric
gray wolf ancestors) to survive in the harsh
Arctic environment and other cold areas of northern Eurasia and North America, which are both very dry and very cold. 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. 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.{{cite journal |author=Ruben, J.A., Hillenius, W.J., Geist, N.R., Leitch, A., Jones, T.D., Currie, P.J., Horner, J.R., and Espe, G. |title=The metabolic status of some Late Cretaceous dinosaurs |journal=Science |date=August 1996 |volume=273 |issue=5279 |pages=1204–1207 == See also ==