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Re: Great in the air, not so good underwater

----- Original Message ----- From: "Michael Habib" <mhabib5@jhmi.edu>
To: <dinosaur@usc.edu>
Sent: Sunday, December 10, 2006 7:03 PM
Subject: Re: Great in the air, not so good underwater

Hmmm. Does your measurement of wingloading in paleo-fliers have an error below +/- 10%? What is the of the error in measuring wingloading in extants?

For some, mass can vary by about +/- 25% from the average during the course of a long flight, not counting errors in planform measurement. Since planform also varies throughout the flapping stroke and also during the moult, that's sort of a hard question to answer. Loading varies with time.

Also, if you actually mean just comparing the extinct flying species to extant ones, the difference in mass to be accounted for is much more than 2 fold. I was comparing the largest flying birds (fossil forms) to the largest pterosaurs (the largest pseudodontorns were probably about 60kg in mass. I've seen estimates for Argentavis around 80kg, but I have not calculated it for myself.

Nor have I, but the most convincing estimates were about 75 Kg, +/- perhaps 25%.

Quetzalcoatlus northropi, by comparison, could easily have exceeded 200 kg, and likely more than that).

Qn could have flown at that weight, but it would not have been an optimal loading for the planform. About 150 Kg, seems more probable.

I note that the 12-14% O2 increase in the Cretaceous only translates to a 2.5-3% increase in overall air density (given that O2 is about 21% of the atmospheric contents by mass). Since Re (and load carrying capacity) will increase in direct proportion to density, that is only about a 3% load jump, and insufficient to explain the 2.5 fold difference in mass between the largest birds and the largest pterosaurs.

I think the mass difference between birds and pterosaurs may have been closer to 2 fold. I agree about the load jump, and note in passing that modern birds often depend upon aerobic power for the muscles (with the exception of launch and perhaps short periods of hover with the flutter stroke). Pterosaurs don't appear to have quite that dependence because of the intermittent flapping (yes, I realize that many birds are intermittent flappers too).

All the best,
P.S. I'm losing track of who is saying what too.