Turbinate bones

Other animals

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. However, objections have been raised against this argument. Nasal turbinates are absent or very small in some birds, such as ratites, Procellariiformes and Falconiformes. They are also absent or very small in some mammals, such as anteaters, bats, elephants, whales and most primates, although these animals are fully endothermic and in some cases very active. Furthermore, ossified turbinate bones have been identified in the ankylosaurid dinosaur Saichania.