Re: Campbell's even crazier than a MANIAC? (archeopteryx

[dinoboygraphics@aol.com]

Mike knows this but it's worth noting that power output is not the only 
limiting factor on distance flight.  Aerobic capacity must be sustained 
for the duration as well, and it would probably behoove us to spend 
more time on when the aerobica capacity for sustained edurance flight 
showed up rather than
if the muscle power and lever arms were in place (flight itself it 
likely to have preceeded the capacity to fly across time zones...).

Several papers have pointed to the importance of the pelvi air sacs, 
hinged sterna (and possible a concurrent loss of gastralia) and a few 
other characters as being related to allowing ventilation to occur 
efficiently alongisde the forces placed on the rib cage during flight, 
in which case sustained flight.  I think more work needs to be done, 
but the aerobic limits to distance flight seem to me to be a more 
fruitful avenue to pursue.

My guess (and I suspect HP Holtz's) is that earlier avian evolution was 
limited to short duration flight...although for the reasons Mike has 
described referring to it as "burst flight" is not appropriate.  
Especially once you can WAIR up a tree, short duration flight becomes a 
handy way of getting around, and extending control and timing over your 
landing provides a clear selective path towards a more modern flight 
apparatus.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3
466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message-----
From: Michael Habib <mhabib5@jhmi.edu>
To: dinosaur@usc.edu
Sent: Fri, 26 Sep 2008 9:56 am
Subject: Re: Campbell's even crazier than a MANIAC? (archeopteryx


Thomas R. Holtz, Jr. wrote:Â
Â
> For myself, I think that far too many people extrapolate a neoavianÂ
> (non-tinamou, non-galliform) flight ability too far down within the > 
historyÂ
> of birds. Based on flight distribution of living birds, I consider it 
> quiteÂ
> likely that good long distance flight may have been limited to > 
anseriformsÂ
> (and not sure how far down it goes among these) and in Neoaves, and > 
thatÂ
> basal members of Aves/Neornithes may have had a more limited flight > 
scope.Â
Â
This depends on how basal you go. Sustained flight over distance seems 
plausible for basal Ornithurans, at the least - the flight apparatus of 
Gansus is actually quite consistent with a sustained flyer (though not 
with the power of an anseriform). As I mentioned earlier, the 
distribution of flight characters in the Neornithine phylogeny can be 
misleading regarding the basal state, in part because of the loss of 
diversity in Paleognaths (their stronger flyers are extinct) and the 
fact that galliforms happen to be rather basal (but they only have 
limited flight range because they're burst launchers - a highly 
apomorphic state).Â
0AÂ
Keep in mind that many living long-distance flyers have rather limited 
flight muscle fractions (12% or so). Loons and grebes can fly rapidly 
over distance, and have quite small muscle fractions. In addition, 
because rapid, aerobic flight over distance doesn't require 
particularly high power outputs, nor large flapping amplitudes, the 
required forelimb skeletal strength is also quite modest.Â
Â
Anseriforms buck this trend a bit, and have much larger sterna and 
somewhat stronger forelimbs than other endurance flyers. They also 
cruise at very high speeds, but this all relates to a much larger 
muscle fraction: 23-26% or so for many species. Interestingly, loons 
reach high cruising speeds with about half this fraction, and also 
cover long distances, indicating that the large muscles of ducks and 
geese are important for more than just rate of flight or endurance 
ability (it may relate to launch and maneuvering, but more on that some 
other time).Â
Â
Based on structural strength and approximate muscle volumes, I see no 
reason to think that distance flight was not present in many of the 
birds more basal than Neornithines (though certainly not present near 
the base of Aves). On the other hand, very few (if any) are likely to 
have had the power output of anseriforms.Â
Â
> But as the long term success of (among others) galliforms show, being 
aÂ
> successful flying bird doesn't mean you have to20fly as well as a 
crow, > hawk,Â
> or heron!!Â
Â
True, though galliforms are actually better flyers than your average 
crow, hawk, or heron in some ways - they've given up endurance flight 
for improved burst performance and slow flight ability, and this 
actually requires expanded power, and a more derived shoulder and 
sternal morphology. Few, if any, more basal birds seem to fit this 
burst model (perhaps Piksi). On the flip side, while herons and kin may 
be good flyers, they do so with rather limited muscle fractions, and 
pretty standard shoulder excursions. Herons also get away with very 
limited structural strength in forelimbs and hindlimbs (they manage 
this with low wing loadings, and thus limited launch speed requirements 
- this then allows for the limbs to be long and gracile, which 
synergizes with wading ecology). So the structural and power 
requirements are not as steep as they might seem.Â
Â
I agree that many basal birds likely lacked the power and/or distance 
scope of modern Neornithines, but it depends entirely on how basal we 
go. The mechanical evidence does not support the conclusion that 
distance flight is limited to Neornthines , though the extreme cases 
(like ducks) are probably limited to the crown group. In this 
particular case, the EPB is probably misleading.Â
Â
Cheers,Â
Â
--MikeÂ
Â
Michael Habib, M.S.Â
PhD. CandidateÂ
Center for Functio
nal Anatomy and EvolutionÂ
Johns Hopkins School of MedicineÂ
1830 E. Monument StreetÂ
Baltimore, MD 21205Â
(443) 280 0181Â
habib@jhmi.eduÂ