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.
Both remaining groups of therapsids, the therocephalians and the cynodonts, became increasingly mammallike in appearance during their evolution.
Previously, no ridges for potential respiratory turbinals have been described for therocephalians.
It is therefore entirely possible that this turbinal attached to the ventral portion of the nasal in therocephalians.
It is not known at present whether other therocephalians possessed respiratory turbinals.
Cynodonts supplanted the gorgonopsians and therocephalians as the dominant therapsids during the Early Triassic Period (Kemp 1982; Carroll 1988) and persisted throughout the Triassic and into the Jurassic.
Ridges probably associated with respiratory turbinals first appear among advanced therapsids, the therocephalians and cynodonts.
However, the maxilloturbinal ridges in therocephalians and cynodonts suggest that ventilation rates in these taxa had increased substantially.
The combination of these two features suggests that although the respiration rates of early therocephalians had already increased sufficiently beyond "reptilian" rates to cause significant respiratory water loss, progress towards "mammalian" levels of respiration was still relatively modest.
If early therocephalians possessed only moderately elevated ventilation rates, the same was likely also true for the first cynodonts.
Thus, aerobic capacities and stamina of therocephalians and cynodonts could have undergone their apparently gradual expansion without the adaptive "valleys" associated with the "thermoregulatory" scenario.
However, in a recently prepared specimen of the primitive therocephalian Glanosuchus (GS M796), an additional ridge occurs ventral to the nasoturbinal ridge on the lateral wall of the nasal cavity.