Heretofore, no evidence for the existence of strictly respiratory turbinals has been described for mammallike reptiles, although they are known in early mammals (e.
Several newly prepared fossil specimens are described, which suggest that respiratory turbinals did, in fact, occur among therocephalians and cynodonts, two groups of advanced therapsids.
Embryonically, the conchae and turbinals of all higher tetrapods develop from folds of the cartilaginous nasal capsules (Goodrich 1930; Matthes 1934; Parsons 1970; Moore 1981).
The respiratory turbinals of birds also appear capable of reducing respiratory water loss (Schmidt-Nielsen et al.
Nevertheless, at this time not enough is known about the effect of strong air currents on olfactory epithelium to support a close, functional association between these turbinals and endothermy.
Avian turbinals probably have respiratory and olfactory functions analogous to those of mammals.
The locations of these basal ridges reflect the functions of the turbinals as well.
Like the turbinals of the prefrontals, however, these would have been primarily olfactory in function.
The many olfactory turbinals in gorgonopsians suggest that these animals had a comparatively well-developed olfactory sense but says little about their ventilation rates.
It is not known at present whether other therocephalians possessed respiratory turbinals.
Respiratory turbinals are found only in mammals and birds, and their function, at least in mammals, but probably in birds as well, is to reduce the respiratory water losses associated with rapid and continuous pulmonary ventilation, a fundamental component of endothermic physiology (Hillenius 1992).