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Re: SPECULATION: pterosaur extinction versus bird survival



Demetrios Vital wrote:

 Pterosaurs also had a less efficient breathing system than
birds.

James R. Cunningham wrote:

 Some pterosaurs had necks that were between 5 and 10 feet long.  Any animal
that can recycle a column of air that long while in flight has a pretty
sophisticated breathing system.

Demetrios Vital replies:

Yeah, they had an efficient breathing system--but notice I said "less
efficient...than birds."  I say this for several reasons.  One is the neck
itself.  Pterosaurs have notoriously small bodies and very long necks.  Yes,
they could recycle that column of air, but how many breaths does it take to
completely recycle it?  I do not know whether pterosaurs used a
pseudo-diaphragmic system, or an air sac system, but no matter what they
used, something in their torso has to expand.  Their ribs and/or diaphragm
can only expand so far, can only exchange so much air.  This is true of
birds as well, but it their system is more efficient for the following
reasons.  One, birds were smaller, so it is easier to recycle the volume of
air they require.  Two, they have generally shorter necks, so a still more
efficient amount of air is recycled.  Three, their larger pectoral muscles,
shorter necks, and wider wings allow for the wing beats to accompany the
breathing by acting as a bellows, and further increasing the recycling and
efficiency of their breathing.

The breathing abilities of the animals at the end of the Cretaceous is, in
my mind, a more than major explanation for the extinctions of the respective
families.  Non-avian-dinosaurs and pterosaurs had less efficient breathing
systems than birds.



James R. Cunningham wrote:

What about the ones that weren't 'ocean gliders'?  It would appear that both
Q species and Q northropi would be capable of flight in today's atmosphere.
However, it does seem likely that soaring conditions would have been
disrupted from a few months to a few years after the K/T transition, and
that should have been enough to do in a soarer.  Are any soaring birds known
to have existed during the late K, and if so, did any of them survive the
transition?

Demetrios Vital replies:

I have heard of no small pterosaurs that lived up to the K-T boundary.  I
have also heard of no soaring birds on the magnitude of Maastrichtian
pterosaurs, either (I know that no birds approached _Q. northropi_ in
wingspan-I just mean big soaring birds).



Demetrios Vital wrote:

The two different types of wings alone seem to indicate birds being better
fliers at a lower density.  And because they are lgihter, they didn't need
the density as much.

James R. Cunningham:

I don't follow your line of reasoning.  Would you expound on this a bit?

Demetrios Vital replies:

Sorry I was unclear.  Here goes...  Longer, stiffer, thicker wings are
better suited to fly in denser atmospheric conditions.  The Boeing 747 has
to achieve a very high speed to fly with its wings and size.  A _Q.
northropi_ today would also have to achieve higher speeds or strong wind
currents to fly efficiently.  In the Cretaceous, however, my theory is that
not only were oxygen leves higher, but the atmosphere in total was denser.
And it was more dense than our atmosphere by an amount that definitely
affects pterosaur flying.  So because of the denser air and consequently
stronger currents, _Q. northropi_ (again, only an example) would be able to
fly at lower speeds and would need to expend less energy to do so, than if
it lived today.

Birds' wing structure, however, obviuously is and was able to accomodate to
the lower atmospheric density, for many reasons.

I hope I've cleared my ststement up.

Peace out, Demetrios Vital