Pterosaur size

[don ohmes <d_ohmes@yahoo.com>]

Re maximal Pterosaurs-- OK, barring
a final question, I’ll wait for the paper, although I appreciate your offers of
access. To verify our points of agreement; the big girls existed (11m or bigger
wingspan), they could fly, and the upper size limits of volancy generally are
constrained by launch and  landing
capability? Guess it's a start. So, anyhow, what are you using for wingload?


 


Re high-altitude migratory
birds-- You cite their performance over a wide range of  altitudes (.59 atm-1 
atm, to use Jim’s
numbers) as evidence these large birds would be unaffected by small changes
(~15%) in average global density.  Relative
to a given process, selection occurs at the point of maximum stress, and it
isn’t surprising that you don’t observe a large change in behavior or
morphology from the point of maximum stress to the point of least stress.  The 
appropriate question is; how will they
perform in a habitat range of .5atm-.85atm, or .68-1.15atms? 


 


 


To use an analogy-- I weigh 100kg,
and like to jog on the beach (boy, I wish, but that’s why I like thought
experiments). Once a week, I run a marathon with 15kg strapped on my back. I am
optimized to running weekly carrying 15 kg, and therefore finish my marathon,
which is good for me ‘cause I’ll die if I don’t. The beach of course, is just
the beach. You observe my performance and notice that I seem to be using 
approximately
the same running style 7 days a week. You reason that I can easily cope with a
15% change in my weight. Wrong. This observation tells you nothing about my
ability to cope with a lifestyle wherein I weigh 115kg on the beach, and 132kg
while running my mandatory Saturday marathon.  Granted, a day at the beach is 
just a day at
the beach, but Saturdays are a bitch. Or more to the point, how much are my
chances of a long life improved if I weigh 85kg and marathon at 98… “small”
improvements in ambient conditions lead to small improvements in athletic 
performance
lead to very large improvement in the probability of success, and by the math,
a bird flying in +15% has lost 15% of its weight. That is the equivalent of the
real me losing 36 lbs. Makes a HUGE difference.


 


IIRC-- Most birds have a large
vertical habitat, and little work has been done, but variations in
wingload/relative winglength in the expected direction have been found in birds
in New Guinea,
and the Andes. Blackbirds that nest at 2500’ have lower
wingloads than sealevel nesters.  


 


BTW, does anyone know what the
maximum observed altitude for landing and takeoff are in Jim’s swans? Seems 
like if you could determine minimum launch density, you could adjust to 
sealevel, and get a eco-perspective on max viable swan size. Or
someone could loadtest an eagle or falcon at various altitudes. Or both. Just 
to check. Checking
is good, right?


 




Another extant maximal volant,
the hummingbird, has a hovering failure density of .49, IIRC. They are very
sensitive to average density changes in the evolutionary sense because they are
the maximal animals in a size-limited locomotive process. However, hummingbirds
can also fly in the flapping style. Note that when they do, they become the
extant minimal flappers. Do you think that their failure density while flying
in flapping style is higher than that of the swan? That would seem to be
predicted by the statement, “small fliers are more affected by medium density
changes than large”. I take your point about weight to density ratios, but from
the ecological perspective, which bird is more likely become extinct or alter
it’s lifestyle if we dial in .85 as sealevel pressure? And which bird has a
large enough functional envelope to remain flexible relative to those two
options? What benefit would accrue to all
the “feeble launchers” and “crash landers” from 1.15 atms?


 


Don