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Re: SPECULATION: pterosaur extinction versus bird survival



Hi Ray, I found this interesting too, and I for one am glad to see you talking
pterosaurs on the dino list (my apologies to the multitude who aren't
interested).  I've interspersed comments below.

Jim

Ray Stanford wrote:

>     It seems likely that the initial impact event would have caused very
> severe winds not only within a few thousand kilometers radius to the impact,

Very likely.  Let me digress for a moment -- I'll come back to your winds, I
promise.  Unless I blink my eyes and forget, that is.  I strongly encourage
everyone interested in the K/T event to read pp 1119-1122 of the December 2000
Geology (G28119.PDF), 'Mass Failure of the North Atlantic Margin triggered by
the Cretaceous-Paleogene Bolide Impact'.  It seems that there may have been
rather massive slope failures in the western Atlantic that were roughly
contemporaneous with the impact event (that is, starting within a few hours and
lasting for a few weeks to months).  It would also seem that the continental
shelf failed from Florida north to the Grand Banks, creating mud and chalk
slides that covered the floor of the Atlantic east to the mid-Atlantic rise, so
that the area between 55W-75W & 20N-43N (1,500,000 sq.mi.) was covered by mud
and chalk flows to a depth of 3.5 to over 50 feet.  Now, this would have long
term effects that would be considerably more catastrophic than the immediate
effects, but I'm going to limit my diatribe to the moment (or to the first few
hours anyway).  The impact, estimated to have been greater than 100 million
megatons of TNT, is estimated to have created a vertical ground swell 50 feet
high within 60 miles of the crater, but I doubt that any nearby animals would
have lasted long enough to be much interested in that.  However, the ground
swell is estimated to have still been over a yard high at a distance of 4300
miles, and up to 10 feet high for a considerable fraction of that.  Now I'm not
all that large, but I'd make quite a thump if someone were to suddenly toss me
10 feet in the air and let me fall back to earth.  Even 3 feet might cause me to
break something. and I'm not sure I'd survive for any length of time if
untreated.  The two pterosaurs that I mess about with both seem to have been
quadrupedal.  If they were on the ground when the ground swell arrived, I wonder
how well their arms would have survived the shock?  Not to mention the resulting
tumble.  As an aside, for an impact of this magnitude it is irrelevant whether
it is an airburst or a ground strike.  It'll still create a crater a couple of
hundred miles in diameter and ionize most every molecule of water in the
vicinity.

> but even world-wide, within a very short time compared to the development
> time of more normal weather/wind systems.

Now, let's think about the tsunamis for a moment.  The subsidence off the
eastern seaboard could be expected to create waves that would travel toward
shore at a speed of a few hundred miles per hour.  Upon nearing the coast they
would slow down and increase in height, reaching the shore at speeds on the
loose order of a hundred miles per hour or so, but with a wave height increased
to the loose order of a few hundred feet to a half mile.  I'd hate to get
slapped by a wave a half mile high going faster than a freight train, but what
I'm really thinking about is the air displaced by that wave front.  Pterosaurs
like Pteranodon and birds like the wandering albatross can fly off the ridge
lift created by normal winds rising over waves only 3-10 feet high.  Think what
the ridge lift from a half mile high wave pushing hurricane force winds in front
of it would do to either of them (yes, I realize that the albatross wasn't
around at the time, lucky rascal).  Though the referenced paper didn't mention
it, somewhat similar effects could be expected in the Pacific.

>   At a somewhat lessened level,
> very severe weather/wind systems would probably have continued, world-wide,
> for weeks or maybe even months.

Try years or decades.  When you suddenly put somewhere around 30,000 cubic miles
of extra water vapor in the atmosphere it helps drive a heat engine that takes
quite a while to disperse, particularly since the hydrologic cycle will process
the water through several complete cycles before things get back to normal.

> And, when one compares the very long, slim wing
> structure of at least the larger pterosaurs known to exist up to the K/T
> boundary to the wing structure of birds that existed in the same period,
> might one find at least part of the reason that pterosaurs did not make it
> through impact related severe winds, while various birds did?

Yeah.

>  Make a comparison for yourself, and I suspect this list's own Jim Cunningham
> might
> help some of us understand the differences in pterosaur wing vulnerabilities
> versus bird wing vulnerabilities, when such structures are subjected to
> hurricane force (and higher) winds while the animals are in flight or
> attempted flight (such as during take-off).

You said it well enough for both of us.  I can't improve on that and am not
going to try.

>     In short, it seems to me that pterosaur wing-bone structure (and,
> possibly, in-flight deployment strategy) might well have been the Achilles'
> tendon that left pterosaurs fatally vulnerable to very strong impact-related
> winds, yet with some birds relatively free of damage.

Quite so, with the key phrase being 'very strong'.

>     Also, anyone who has studied pterosaur trackways becomes quickly
> impressed by the much deeper impressions invariably left my the pterosaur
> manus (hand) than by the pes (foot).

Ray's not exaggerating about this.  The hand carries a lot more weight than the
foot.

> A pterosaur with a wind-snapped wing
> bone not only could not fly, but would have been hard-put to even maintain
> terrestrial locomotion.

And if he were within a few thousand miles of the impact, the ground itself may
have whacked him hard enough to break something.

> Pterosaur vulnerability is my emphasis
> here.

I too see pterosaurs as being far more vulnerable to permanent damage from
super-hurricane force winds, because of their less tightly folded wings.  Chris
Bennett reads this list, and he knows more about pterosaur bone structure than
maybe anyone else in the world.  Chris, do you have any thoughts about this?

>   Pterosaurian wing carriage (whether as
> interpreted by our own list's David Peters or by David Unwin) would
> certainly have made an on-the-ground Late Cretaceous pterosaur far more
> vulnerable to very high winds, than how those same winds might have effected
> an Early Cretaceous bird with its different wing carriage.

The pterosaurs did have a lot more area stuck out in the breeze.

>  Or, does anyone out there
> have a more plausible explanation of how birds survived the K/T boundary
> event while pterosaurs did not?

I think you're pretty much on target, but I'd like to add that most pterosaurs
seem to have been more heavily dependent upon soaring than were most
late-Cretaceous birds, and you could expect soaring conditions to be pretty
crappy for a few decades after the impact.  On the other hand, conditions for
flapping flight would become marginally acceptable pretty quickly.