Re: Theropod respiration questions

["Guy Leahy" <gleahy@bellsouth.net>]

        I can't comment on Tracy Ford's article, since I haven't seen it.
In birds, the long posterior thoracic and abdominal ribs ventilate the
airsacs, not the lungs.  In birds, the lungs are very stiff, and volume
changes as a result of ventilation are minimal.  In fact, in some birds the
anterior thoracic ribs actually form indentations in the lung.
        The acquisition of similar rib cages in carnosaurs and coelurosaurs
suggests a similar type of lung may have been present.  The presence of
pneumatic caudal and/or sacral vertebrae in oviraptorosaurs, tyrannosaurs,
_Acrocanthosaurus_ and _Carcharodontosaurus_ (thanks, Dr. Holtz, for the
additional examples,)  suggests the presence of abdominal airsacs in these
theropods.
        The avian-like ribcage design I described in the Sci Am book appears
to be restricted to Avetheropoda at this time.  More basal theropods, such
as _Coelophysis_, lack most of these features.  The presence of long
anterior trunk ribs and pneumatic foramina restricted to the cervical +
anterior thoracic vertebrae in such theropods suggests they possessed only
cervical airsacs, and that the lung was still flexible enough to be
ventilated by the ribs.
        Uncinate processes occur in vertebrates with widely disparate lung
types (_Sphenodon_, crocodilians and birds,) so such processes do not appear
to be linked to any particular lung design.
Ossified uncinate processes have been hypothesized to stiffen the
ribcage in order to better withstand the mechanical stresses of powered
flight.  I'm not aware if anyone has ever tested this experimentally, but a
few flying birds (screamers) lack them entirely.
        It's interesting to note that birds, unlike nearly all mammals (with
the exception of humans,)  are not invariantly coupled to a one breath/one
locomotory cycle.  Birds frequently exhibit 1/1 respiratory/locomotory
cycles, but they are not mechanically constrained to this frequency.

Guy Leahy


----- Original Message -----
From: "Dino Guy and Computer Gal" <gbabcock@best.com>
To: "Guy Leahy" <gleahy@bellsouth.net>
Cc: <dinosaur@usc.edu>
Sent: Monday, September 24, 2001 11:39 AM
Subject: Theropod respiration questions


> In Guy Leahy's article, "Noses, lungs, and guts," from Gregory S. Paul's
> _The Scientific America Book of Dinosaurs_, Leahy describes the
> osteological characters of non-avian maniraptoran theropod anatomy that
> would correlate with an avian respiratory system: double headed ribs,
> short anterior trunk ribs, long mid-trunk and lumbar ribs, large
> ossified sternal plates (with articulating facets for five sternal ribs
> in _Sinornithosaurus_), highly excavated neck and anterior trunk
> vertebrae (and pelvis and caudal vertebrae in _Oviraptor_, suggesting
> abdominal air sacs).  Tracy Ford's recent article in _Prehistoric Times_
> on gastralia puts forward the hypothesis that gastralia featured sliding
> linkages which would have enabled theropods to expand and contract the
> abdominal space in order to pump air through the respiratory system.
>
> Taken together, these observations (and related functional hypotheses)
> offer an x-ray view of the theropod torso as a dynamic cage of intricate
> linkages that would provide considerable expansion and contraction,
> facilitating highly efficient respiration for these (apparently) very
> active animals.
>
> Questions:
> What muscles would control these articulations?  Where are these muscles
> located?
> Would the rib cage contractions synchronize with contractions of the
> gastralia, or would the ribs contract the pectoral portion of the torso
> while the gastralia expand the abdomen?  Would it make any difference?
> What respiratory function (if any) do uncinate processes serve?
>
> -- Ralph W. Miller III   ralph.miller@alumni.usc.edu
>
> (ignoring for the purpose of this discussion the hypothesis that
> _Sinosauropteryx_ utilized preparator's glue to facilitate lung
> ventilation)...
>
>