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

[Michael Habib <mhabib5@jhmi.edu>]

Thomas R. Holtz, Jr. wrote:

> For myself, I think that far too many people extrapolate a neoavian
> (non-tinamou, non-galliform) flight ability too far down within the 
> history
> of birds. Based on flight distribution of living birds, I consider it 
> quite
> likely that good long distance flight may have been limited to 
> anseriforms
> (and not sure how far down it goes among these) and in Neoaves, and 
> that
> basal members of Aves/Neornithes may have had a more limited flight 
> scope.

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).

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.

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).

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.

> But as the long term success of (among others) galliforms show, being a
> successful flying bird doesn't mean you have to fly as well as a crow, 
> hawk,
> or heron!!

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.

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.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu