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SPECULATION: pterosaur extinction versus bird survival
Hopefully I may be forgiven for discussing pterosaurs on a dinosaur
list, but some speculation concerning possible contributing factors to
pterosaur extinction coincident to the K/T boundary event(s) comes to mind.
"Event(s)" is used here in reference not only to the impact event, per se,
but to various environmental changes initiated by it over an undetermined
period of time.
Please consider what follows as speculation or questions about what
might, conceivably, have happened, rather that as established fact:
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,
but even world-wide, within a very short time compared to the development
time of more normal weather/wind systems. At a somewhat lessened level,
very severe weather/wind systems would probably have continued, world-wide,
for weeks or maybe even months.
Pterosaurs did, in fact, live right up to the K/T extinction, as
evidenced by the remains of the gigantic Quetzalcoatlus species found in the
Javelina Formation of Texas' Big Bend area, along with bones of various
non-avian dinosaurs. 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? 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).
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.
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). A pterosaur with a wind-snapped wing
bone not only could not fly, but would have been hard-put to even maintain
terrestrial locomotion. By contrast, I have seen various kinds of birds do
a pretty good job of walking around with a broken wing, and suspect that
Late Cretaceous birds might have done about equally as well, but I am not
implying that being able to walk around with a broken wing was the reason
for bird survival of the K/T event. Pterosaur vulnerability is my emphasis
Further, pterosaur wing placement beside the thorax, whether during
sitting or walking on the ground, would have been substantially different
from that of a bird's wing carriage. 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.
So, could this be at least one of the predominant reasons (if not the
major one) that pterosaurs did not make it through the K/T boundary events,
while birds came through? Is there some fault in my reasoning here? If,
so, I would like to have an explanation of it. Or, does anyone out there
have a more plausible explanation of how birds survived the K/T boundary
event while pterosaurs did not? (But I am not implying that if one does not,
my speculation is, thereby, in any way reinforced.)
Thanks for listening,