Re: Pterosaur size (Was: Great in the air, not so good underwater)

[don ohmes <d_ohmes@yahoo.com>]

Yep. Stuff gets lost, too. So, some correction and re-iteration.

1). The O2 pulse hypothesis calls for a 12-15% minimum increase in _overall_ 
air density, resulting from an approximate doubling of a paleo-O2 partial 
pressure of 15%, with a postulated max O2 atmospheric fraction of 35% (if 
memory serves). I used 10-12% density increase because it is a conservative 
figure relative to the hypothesis. My remarks were directed only to flight 
benefits derived from the increase in air density, _not_ to O2 related 
mass-specific power effects.

2). The reason I used the O2 pulse hypothesis is because it is the only
published, peer-reviewed geochemical mechanism for increasing air density at any
point in post-Archean time that I know of. Note that density is a function of 
total air mass, and can be independent of composition.

3). The observations I made on the fruit flies were taken in the course of
an experiment on selection and obviously need to be replicated.
Anyone who wishes to do so should contact me, because building a tube
(even one that is _not_ pressurizable) those little guys will fly (and  _not_ 
crawl) up is
not as simple as it sounds, and I can increase your chances of success. (But be 
prepared to be patient, if you want pictures.) Minus the vacuum pump and the 
fluon, $100 should do it, so it ain't that expensive, if you own a few tools. 
The flies are free, if you got a banana...

4). "Atmospheric effects" as Habib aptly puts it, do _not_ exclude such things 
as novel launch systems or climate regimes (see Campbell re Argentavis 
evolution and takeoff), anymore than the K/Pg event means that dino diversity 
was not already in decline from other mechanisms. In my opinion, the more 
extreme animals would have needed all the help they could get, even at 1.2 
atms. Now, at 1.5 or 2 atms... }: D

5). It has been 10 years since I searched the data relative to birds. My 
impression at that time was that higher apparent wingloads were the rule in 
paleo-birds of pigeon-size or larger, not the exception. Limnofregata ( from 
Storrs Olson) is perhaps the most accessible example of what I mean. Please 
correct me if I am wrong. Must be a wealth of new material.

6). Yep. Wingload is real hard to measure, and takes a large sample in living 
animals. It seems to me that the various ratios that can be taken within and 
among skeletal components are the best way to go, if complete skeletons and 
similarly-sized NLR's are available. Intuitively, I would say that 
passerine-sized birds would be harder to compare than larger, but I don't 
really know.

7). I've seen (Campbell's original) estimates on Argentavis of 120 kg. My 
impression at the time was that his revision to 76 kg was prompted mainly by 
'aerodynamic objections', but I well could be wrong. Re-do's are always good...

Short on time, again. I want to talk more about flight benefits/body size/air 
density curves...

Be back next weekend, if not before.

Don

PS-- How big would a ptero or bird have to be to elicit a "OK, these guy's had 
to have had some help, because there is just no way in standard atmosphere..."? 
Actually a serious question.


----- Original Message ----
From: MICHAEL HABIB <habib@jhmi.edu>
To: dinosaur@usc.edu
Sent: Monday, December 11, 2006 9:08:47 AM
Subject: Pterosaur size (Was: Great in the air, not so good underwater)

> >  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.

Gotcha; that seems reasonable.  I was going for the upper end (full fuel load, 
etc) to make the point about how much of a mass difference we might need to 
account for.


> 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).  Pt
of 
> the intermittent flapping (yes, I realize that many birds are 
> intermittent 
> flappers too).

I've also noted that aerobic power tends to be the norm for most birds during 
steady state.  Use of anaerobic power during launch can be very important, 
though, especially in birds in which anaerobic burst launch is actually the 
primary flight mode (galliforms especially).  As for intermittent flapping, 
there are only a few groups of living birds (ie. soaring specialists) that can 
utilize intermittent flapping to the degree that large pterosaurs could.  Both 
the convective soaring groups and marine soaring groups of modern birds 
inherited a mostly aerobic power system from their immediate ancestors.  It may 
be that they have secondarily derived higher anaerobic power, but I don't know 
if this has been rigorously studied or not.  Even among pelagic seabirds, I 
suspect only a few would really be under strong selection for greater anaerobic 
fiber ratios; albatrosses are the obvious ones.  Taxa like sulids would receive 
less of a benefit, because they really balance extended soa
ring with significant use of high-efficiency flapping gaits (especially very 
low-amplitude continuous vortex gaits).

> P.S.  I'm losing track of who is saying what too. 

Yeah, it gets jumbled very quickly.  Oh well.

Cheers,

--Mike H.