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



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