Here, the Harvey O. Banks Pumping Plant lifts water 224 feet (68 m) into the California Aqueduct. The resulting evaporative water loss varies greatly and depends on several factors including air sac pressure and the subsequent rate of air flow through the trachea. However, this morphology varies among bird species. If the developmental sequence found in bird embryos is a guide, air sacs actually evolved before the channels in the skeleton that accommodate them in later forms. The morphologies of the individual air sacs also vary among bird taxa. Avian pulmonary air sacs are lined with simple epithelial and secretory cells supported by elastin connective tissues. In penguins, air sac volumes are constricted in deep dives to protect from the effects of water pressure. Birds such as parrots have different air sac arrangements. Very few formal rebuttals have been published in scientific journals of Ruben et al.’s claim that dinosaurs could not have had avian-style air sacs; but one points out that the Sinosauropteryx fossil on which they based much of their argument was severely flattened and therefore it was impossible to tell whether the liver was the right shape to act as part of a hepatic piston mechanism. Historically, desalination was deemed too expensive to be considered a viable large-scale option; it simply required too much energy.

A further indication for the presence of air sacs and their use in lung ventilation comes from a reconstruction of the air exchange volume (the volume of air exchanged with each breath) of Plateosaurus, which when expressed as a ratio of air volume per body weight at 29 ml/kg is similar to values of geese and other birds, and much higher than typical mammalian values. Gas exchange occurs at the parabronchi. No gas exchange occurs within them. In birds, some temperature control occurs in the respiratory system. Instead, voluminous expansion occurs in the air sacs. However this does not explain the expansion of air sacs in the quadrupedal sauropods. Early sauropodomorphs, including the group traditionally called “prosauropods”, may also have had air sacs. In a species of tyrannid (the sister group to true songbirds), birds have two different sources of sound around the trachea. At high air sac pressures, the two sound sources have different frequencies, while at low pressure they have the same frequency. Cancer and Aries also have some synergy in the career arena.

Researchers have presented evidence and arguments for air sacs in sauropods, “prosauropods”, coelurosaurs, ceratosaurs, and the theropods Aerosteon and Coelophysis. They also presented this as a reason for doubting that birds descended from dinosaurs. Birds have a system of air sacs in their ventilation system. These pneumatic bones are less vascularized than non-pneumatic bones and many pneumatic bones have pneumatic foramina (openings for air passage). The air sacs are usually paired, except for the clavicular air sac, creating a total of 9 air sacs. Different air sacs alternate contraction and expansion, causing air motion, the fundamental mechanism of avian respiration. The pressure in the interclavicular air sac is highly correlated with the fundamental frequency of birdsong in doves. Air sacs play a role in song production in songbirds and related birds, with some studies hypothesizing that the air sac may be involved as a resonating chamber. The portion of the neural pathways which control respiration during vocalization changes air sac pressure to control vocal intensity. In diving birds, the air sacs can aid in helping birds with respiration.

Pneumatization of the skull (such as paranasal sinuses) is found in both synapsids and archosaurs, but postcranial pneumatization is found only in birds, non-avian saurischian dinosaurs, and pterosaurs. So far no evidence of air sacs has been found in ornithischian dinosaurs. Aerosteon, a Late Cretaceous megaraptorid, had the most bird-like air sacs found so far. Bone pneumaticity is generally found in the appendicular skeleton. It is found that when air moderately impregnated with carbonic acid is inspired it greatly impedes the exhalation of more from the lungs; and that the greatest quantity of carbonic acid which exists in prebreathed air never exceeds 10 per cent. Many biodiverse species have long lifespans on the seafloor, which means that their reproduction takes more time. But this does not imply that ornithischians could not have had metabolic rates comparable to those of mammals, since mammals also do not have air sacs. The air sacs work to produce a unidirectional flow where air enters and exits the lung at the same rate, contrasting the lungs of other tetrapods such as mammals where air enters and exits the lung in a tidal ventilation.