The anterior turbinal is usually relatively simple, but the others, especially the middle turbinal, are often more highly developed into prominent scrolls with multiple turns (fig.
The middle turbinal is usually the largest and most elaborate in the avian nasal cavity (fig.
The maxilloturbinal is the most extensive and complex mammalian turbinal element.
Significantly, in birds, too, the olfactory posterior turbinal is usually positioned outside the respiratory airstream and even may be situated in a blind recess in forms with a well-developed sense of olfaction.
In life, the duct continues forward along the base of the turbinal to its opening in the floor of the nostril near the anterior part of the maxilloturbinal (Evans and Christensen 1979; Nickel et al.
Typical mammalian turbinal attachment ridges occur on the maxillary, nasal, and frontal bones.
The presence in these animals of an essentially mammalian turbinal complex, inclusive of extensive respiratory maxilloturbinates, therefore strongly indicates that even the earliest mammals possessed high ventilation and oxygen-consumption rates, similar to those of modern mammals.
Among the reptilian ancestors of mammals, turbinal ridges appear to go back as far as early pelycosaurs, the oldest (Late Carboniferous and Early Permian Periods) and most primitive group of synapsid reptiles.
In contrast, no turbinal ridges are found in the respiratory portion of the nasal cavity.
Tatarinov (1963) disagreed, however, and considered the ridges turbinal supports instead.
These ridges have been associated with the sphenethmoid complex by some (Barry 1967; Cluver 1971) but are interpreted by others as turbinal ridges (Kemp 1969, 1982; Cluver 1971).
Several longitudinal ridges occur in the gorgonopsian nasal cavity, which are interpreted as turbinal ridges (Kemp 1969).
Among therocephalians, turbinal ridges have been noted along the roof of the nasal cavities of Akidnognathus (Brink 1960) and Moschowhaitsia (Tatarinov 1963).