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Re: THEROPOD-BIRD RESPIRATION



Greg said (28 Feb 99):

>Theropods progressively
>developed the skeletal features associated with and required by avian
air-sac
>ventilation. These included short chest ribs, elongated posterior ribs with
>mobile double heads, a deeply corrugated ribcage ceiling, and pneumatic
>vertebrae. The most bird-like theropods also had an elongated sternum with
a
>hinged coracoid articulation, ossified sternal ribs and ossified uncinate
>processes -

       >all of these avian features are absent in even Archaeopteryx.  [my
emph.]

>As I pointed out at Yale, one could hardly ask for a better example of
>progressive evolutionary development. In contrast the theropod liver pump
>has no evolutionary context, and no compelling evidence supports it.


If in Ax the full bird-breathing system is not yet developed, and it didn't
use the diaphragm or liver-piston systems either, presumably it must have
used the default theropod system.  Do we yet have any idea how this worked?
It can't have been the one used by reptiles today.  Presumably it was an
early version of the bird system, and if so, perhaps those features that Ax
lacked weren't so much associated with breathing as with flight (though a
more rigid thorax would presumably allow lower pressures on the inbreath,
and thus more forceful breathing).



Phillip Bigelow <bh162@scn.org> wrote:

>
>About 10 years ago, Martin called the posture of Archie "like that of a
>primate" ("The case of the flying dinosaur", _NOVA_, PBS videos).
>Presumably, according to Martin, this was to afford the animal a center
>of gravity very close to a tree trunk.  I haven't heard if he has since
>revised his ideas on this.
>
>If Archaeopteryx did have a primate-like posture, it is the only
>archosaur known to have had one.


In monkeys, the primate-like posture corresponds to vertical trunk when
climbing vertical trunks, and sub-horizontal when on the ground.  As with
many climbers (woodpeckers, squirrels) etc the one doesn't preclude the
other.