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Re: postulated bird/pterosaur competition... with a little HUMOR (?) at the end :o)




dinotracker wrote:

>  I wonder if especially
> the changing wind patterns, velocities, localized wind-shear effects, and
> temperature changes might have caused, for example, survival problems for
> many pterosaur species appreciably before the K/T terminal event.

Ray, this is all quite speculative.  Those changes appear likely to me to be
what drove the azhdarchidae to large sizes during the later Cretaceous.  During
that period, the big pterosaurs were larger than any birds have ever been, or
are likely to ever be because of structural limitations that affect bird
wingspan more than pterosaurs.  I suspect that smaller birds that used full-time
flapping may have out competed smaller pterosaurs even before the atmospheric
dynamics became more 'intense'.  However, soaring birds couldn't hold a candle
to the larger pterosaurs and I suspect the big pterosaurs may have precluded the
development of large soaring birds until after the demise of the pterosaurs.

>     In situations of wind extremes, I suspect that an 'Achilles tendon' in
> the pterosaurs might well have been the very long, slender, digit IV 'wing
> finger'.  As an adaptation facilitating flight, that item was extremely
> thin-walled and hollow, and served the function well in environments to
> which it was suited. But when winds became very extreme and turbulent it is
> not wild speculation to think that many 'wing fingers' could have become
> broken in flight, spelling certain doom for the unfortunate pterosaur. (A
> wind-induced tear in the flight membrane would have been less likely, I
> suspect, but still potentially fatal.)  It seems to me that the wings of
> birds might be much less vulnerable. What say you, Jim Cunningham?

My talk at the Toulouse pterosaur conference was entitled 'A Skeletal Mechanism
With Application to Automatic Gust Load Alleviation In The Azhdarchidae', so
I've given this a little thought (which doesn't make me right).  The outer
wings, including the cross-section of the phalanges don't appear to me to be
anywhere close to their physical limits in the big azhdarchids, and looking at
the humerus and/or phalange from several different large azhdarchids, I don't
think they were all that close to their maximum possible wingspan either, though
I would start looking askance at estimated spans greater than maybe 42 feet or
thereabouts.  One of the solutions to increasing turbulence is increasing
robustness while also increasing the capability for spanwise twist in the wing,
and the late pterosaurs did just that.  As an aside, were they alive today, they
could launch and fly just fine in today's atmosphere too.  I think birds would
have been able to accommodate a more turbulent atmosphere and changing
conditions, but no better than pterosaurs were able to.  To my mind, the smaller
birds facility at flapping flight may have helped do in the smaller pterosaurs,
and the large pterosaurs facility at soaring may have precluded or helped
inhibit the development of large soaring birds.  As an aside, the limit on
large, full-time flapping in birds appears to be illustrated by the male Whooper
Swan 'JAP', the largest individual bird of any species presently known to fly by
means of full-time flapping.

>     The situation was vastly the more-so if there were any pterosaurs,
> anywhere, that somehow survived the initial devastation of the K/T cosmic
> impact, per se.   Drastically altered oceanic and atmospheric currents would
> have continued for very long periods, and attendant wind strengths and
> directions (to say nothing of acid rains, temperature changes, etc. and
> likely the disappearance of most if not all the pterosaurs' prey from the
> environment to which it was adapted) would undoubtedly have finished off any
> straggling pterosaurs. Considering those circumstances, it seems ludicrous
> to suggest that competition with birds was the culprit!

I suspect that the thing that whacked the last pterosaurs may have been reduced
convection and turbulence in the atmosphere for a short while after the impact.
Pterosaurs can't carry much fuel reserve (no place much to put it), and I think
being grounded for a couple of weeks would have done most of them in from
starvation.  Increased energetics in the atmosphere well after the blast (should
that have occurred -- I don't know that it did) would have been like throwing
Brer Rabbit in the briar patch, but I don't see how they could have gotten
through the initial crunch.  Birds have larger bodies relative to their total
size, can carry relatively more fat, and may have been better able to survive a
period of forced starvation.

>     But I personally think your idea about pterosaur disappearance due to
> bird competition is, well, for the birds! (Pun intended.)

For the smallest pterosaurs, John may have a point, because flapping ability is
relatively more important in smaller animals.  But birds weren't able to outfly
the bigger pterosaurs or even match them, and a bird the size of the biggest
azhdarchids likely wouldn't have been able to launch anyway.  Personally, I
suspect that as gradually changing atmospheric conditions began to favor larger
pterosaurs, the various smaller species either died out or morphed and became
larger for reasons that didn't have anything to do with birds.  I think the
larger pterosaurs also may have helped keep birds from becoming larger (sort of
the inverse of John's view).  All that said, I haven't really made a concerted
attempt to figure out or study in any detail how the atmosphere changed over
time during the Cretaceous.  But, at the end, a short period of relative calm
may have whacked the last remaining pterosaurs -- those that didn't get whacked
by blast effects, tsunamis, etc.