Re: "Acro" ribcage dilemma

["Jaime A. Headden" <qilongia@yahoo.com>]

Jordan Mallon (j_mallon@hotmail.com) wrote:

<<Dale Russell suggests something to the effect that because the
ribcage of _Acrocanthosaurus_ was so narrow, the animal would
have relied solely on an anaerobic metabolism when chasing prey
since it would not have had the capacity to inhale much air in
times strenuous activity.>

  and David Marjanovic (david.marjanovic@gmx.at) wrote:

<Were air sacs taken into account???>

  Airsacs as a rule should not be used to interpret an
organism's respiratory ability based on the faculty of the
bracket-group (crocodile airsacs do not function the same way
that avian ones do, and are much smaller and limited in scope).
The interpretation is a measly "in the middle" untile data
suggests a fixed ribcage is present in dinosaurs and that the
hepatic piston apparatus is qualified/disproven _or_ Carrier and
Farmer's gastral breathing is qualified/disproven.

<AFAIK all theropod ribcages are very narrow.>

  Some theropods have quite rounded ribcages: Spinosaurs,
dromaeosaurids sensu stricto, tyrannosaurs, and basal birds,
where the ribs are well rounded and not strait or curved
transversely.

  The problem with Russell's position, as I see it (I remember
the show) is that the ribcage is so _deep_ that even if the
lungs were narrower relative to *Allosaurus* (they seem so) the
ribcage is that much deeper. See this in *Yangchuanosaurus* and
*Monolophosaurus*, where the deepest ribs descend to the level
of the ventral margin of the pubis. Also note where the deepest
ribs are. The farther back in the costal series they are, it is
possible to assume the farther back the lungs are; this opens up
the idea of avian respiration, somewhat. Also take into account
the width of the pelvic girdle, which limits the width of the
gut as well as the caudal gastral airsacs, in crocs and birds,
so to assume the same in theropods. And sauropods, and
ankylosaurs, and iguanodonts....

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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