Re: Great in the air, not so good underwater

[jrc <jrccea@bellsouth.net>]

----- 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,
Jim
P.S.  I'm losing track of who is saying what too.