dinosaur neck lengths

[JNorton@xxxxxxxxxxxxxxx]

Let me try again.  Last week I posted a query regarding the lengths of
dinosaur necks, and apparently phrased the query poorly.  The
responses centered around bipedalism rather than neck lengths.  Let me
rephrase the question:

The neck lengths of bipedal predatory dinosaurs appear greater than
those of quadrupedal predators (alive or dead) of similar size.  Why?  

I realize that answering this question requires some speculation, but I
would like to hear some speculation from professional vertebrate
paleontologists with knowledge of dinosaur skeletal morphology.  I am a
physiologist interested in paleobiology, which seems to be a field based
on informed speculation.   A long neck comes with a lot of physiological
"baggage" attached, mostly to assure adequate ventilation of the gas
exchange regions of the lung.  A long neck is not the most energetically
efficient means of getting air from the outside world into a lung.  It must
have had other advantages in an active predator with two legs that
were not necessary in a four-legged version.  Incidentally, it would seem
to me (an amateur paleontologist) that a longish neck would have been a
disadvantage in an arboreal creature, if indeed the "trees down" theory
for explaining dinosaur bipedalism and avian flight is correct.

I would appreciate your thoughts.

James M. Norton, Ph.D.
University of New England
Biddeford, ME  04005
phone: (207)283-0171
fax: (207)283-3249
email: jnorton@mailbox.une.edu