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Breathing Apparatus in Tyrannosaurines
The subject of various breathing apparati in extant animals as
applied to dinosaurs is interesting, because there are obvious
alternate systems which may be applied, and I think Ruben et al. 1999
did not confront this. Am hoping to get the article today, so bear my
unread comment on that.
Otherwise, there are apparently various breathing systems employed
by modern animals, including:
hepatic: liver is pushed into lungs to force expelling of breath. --
employed by crocs and lizards(?).
continuous circulation: lungs are rigid, air is forced in and out by
powered airsacs manipulated by movement of muscle compression. --
employed by birds.
diaphragmatic: lungs are flexible and are compressed by movement of
ribs, and expelled by reactive movement of diaphragm. -- employed by
mammals and snakes(?).
grastralic: gastralia compress internal organs to force flexible
lungs to expell. -- ?
I am unsure how turtles do it, but they seem to have had rigid lungs
and ribs and would have to rely on other forces to breathe. Ruben et
al. suggest that the first (hepatic) was employed by crocs and
theropods, but what about those dinosaurs that lacked a mobile pubis
or any other way of compressing the liver?
Take it this way: tyrannosaurs have rigid backs, the pubis could not
induce the position of the liver, and the back could not squeeze down
to force the lungs to move; the gastralia or a continuous ventilation
are the only other proposed breathing mechanisms through which it can
"pump" it's lungs (as well as whatever turtles employ). The hepatic
system doesn't work for tyrannosaurs, and unless I'm mistaken, it
wouldn't for other rigid-backed dinosaurs.
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