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Re: Pterosaur size
On Wednesday, December 13, 2006, at 03:00 PM, don ohmes wrote:
------- Why not? Current atmoshperic conditions wouldn't stress
or any of their ancestral line.......
You keep telling me that, but I'm skeptical. Wingstroke amplitude and
landing speeds are 2 reasons why. The trend I see in the fossil record
is another. Your statements about launch modes are interesting, your
knowledge base is evidently comprehensive, and for all I know you are
right. But I am still skeptical.
Can you cite why, specifically, you are skeptical? I have not seen
anything to suggest that the wingstroke amplitude and land speeds would
not be fine under modern conditions. In fact, the required wingstroke
amplitude at steady state doesn't come out very extreme at all during a
high-speed continuous vortex gait (which almost any large-bodied,
high-aspect ratio flyer would be using; it is the dominant stroke
kinematic system in all pelagic soaring birds). Amplitude should be
higher during steep climbs, but still not problematic. Have you
calculated an estimate of wing amplitude that is extreme, or a landing
speed that seems untenable? --MH
The physical properties of the atmosphere constrain many processes,
including flight. It is my opinion that a slow directional change in
the physical properties of the atmosphere provides the best fit for
the fossil record as a whole. In my opinion, the direction is such
that "tomorrow" (say, 10 mys) will be even less pterosaur-friendly
I think you may be overestimating the magnitude of the atmospheric
differences, as well as their effects. A 15% overall density
difference will result in relatively minor flight adjustments for a
medium to large-bodied flying vertebrate. Such adjustments would be
well within an individual's ability to alter planform during flight.
They might not even have to do that, depending on the specific animal
in question (and its kinematics). --MH
But it is there. You may feel that it is irrelevant, and you may be
right to dismiss. But it is there.
Largest volants in time sequence: Q. n, various pseudodontorns, A.
mag, Pseudodontornis, T. incredibilis, T. merriami, California Condor.
In wing span sequence: Q. n, A. mag, various pseudodontorns,
Pseudodontornis, T. incredibilis, T. merriami, California Condor.
If you accept that the trough after K/Pg is caused by a catastrophic
event, and smooth accordingly, you get a distinctly non-fluky looking
curve that is ~100 mys long, without need for any statistical
manipulation whatsoever. The negative correlation of wingspan to time
(past to present) is better than -.95. Corrections appreciated. I find
it compelling. But that is just my opinion. Correlation is strong even
if you punch in some of the comeback kids post-K/Pg...
Point taken; but I would re-run it independent contrasts (or a similar
metric) and see what happens. I am not sure you have sufficient
statistical power to say much just using the largest species. It is
also a bit of an odd metric; a changing average size would be more
telling. In any case, the same trend is just as easily explainable as
a difference in lineages (birds vs pterosaurs and their relevant launch
mechanics) combined with two extinction events (end Cretaceous, Late
Pliocene). Also be careful of assigning directionality; a lot of that
trend is going to be based off the small max size of the modern
interval (California Condor). Due to a combination of historical
patterns of phylogeny and historical patterns of extinction, we are in
a mega-volant lacking time interval. It may or may not be significant
that it happens to be the most recent interval. Thus, some sort of
sensitivity analysis is important. What happens when you leave out the
modern interval? What happens if you tack the Jurassic onto the front
of your trend? --MH