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Re: Science feather strength debate



Oh this is just unbelievable. 

In a message dated 11/4/10 9:54:54 AM, jaseb@amnh.org writes:

<< >>> a 20% difference in mass makes a big difference in aerodynamics and 
>> This is ridiculous. The mass of an individual bird can vary by 20% or 
more 
>> over a matter of hours (if it gorges) or days (as body fat deposits 
vary). 
>> It is common for very long distance migrating birds to start out heavy 
with 
>> fat and lose it by the end of the journey. The bird can effectively fly 
at 
>> the beginning and end of the mission. In any case, as I have stressed 
>> repeatedly in the literature, it is not possible to restore the mass of 
an 
>> individual specimen better than +/- 20% or more because of problems with 
restored 
>> volume, SG, and normal changes in an individuals mass. The problem with 
the 
>> Nudds and Dyke was that they overestimated the mass of the Archaeopteryx 
>> specimen they examined by a factor of about two, Confusicusornis by 
about three. 
> 
> If 20% doesn't matter then I wonder why you bothered adjusting Yalden's 
estimate for the body mass of HMN 1880 by 13% (from 271 to 234g). You also 
spend some time discussing the relative merits of a pectoralis mass between 5 
and 15% of body mass.> 

Jason is being flippantly unscientific. I did not "adjust" the Yalden 
estimate. When I complete a skeletal restoration I normally do a mass estimate 
and the 234 g value is what I happened to came up with for 1880, so I 
published the result. It's the usual technical process.  That the results of 
moi, 
Yalden and Elzanowski are not identical is to be expected especially since it 
is not possible to restore body mass closer than ~20%. That they are so 
similar strongly favors their being close to correct. I spend time discussing 
the possible pectoralis mass range because that 3 fold difference for the 
specific portion of total mass that actually powers the wings most certainly 
does have tremendous importance, duh.  

> Moreover, we would both agree that 20% doesn't matter to extant migratory 
birds with highly derived flight apparatus, but modern birds have a lot of 
spare capacity. They can stoop at 200 mph, hover in mid air, and fly 
thousands of miles! In an animal that is barely capable of aerodynamic 
locomotion, 
like any hypothetical ancestor of birds, 20% could be a crucial difference 
between ascending flight and gliding.>

Since the mass of an individual animal can easily vary this much this claim 
too is flippant. And to repeat, N&D were off by factors of 2-3, not 
0.2-0.3.  
 
> I agree that Nudds and Dyke used mass estimates that are too high and 
rachis measurements that were too small, and that their conclusions must thus 
be reconsidered. But Zheng et al. found that Nudds and Dyke still 
demonstrated that both birds had weak rachises compared to extant birds of the 
same 
mass. I still think they flew, but this contribution by Nudds and Dyke suggests 
that Confuciusornis probably couldn't pull the miraculous maneuvers 
(pouncing on fish and then taking off from the water surface) that kingfishers 
do 
today. >>

How often do I have to repeat this? Can't some of you read? It is 
absolutely impossible to currently restore or compare the feather strength and 
therefore flight performance of any Archaeopteryx specimen because in none are 
the 
feather base shafts whose diameter must be measured preserved!!! Give it 
up, the data is simply not available. For the N&D method to be applied to the 
urvogel will require the discovery of a new specimen with the primary 
feather bases preserved. Let us hope even as we do not hold our breathes (Zheng 
et 
al say that only 4 of their 536 Confuciusornis specimens have good feather 
bases). 

And Zheng et al. did not reanalyze Archaeopteryx. 

As for the Zheng et al. reestimate for Confuciusornis feather strength they 
are - obviously -- way too pessimistic because they -- hello -- assumed 
that the N&D 3 times too high mass estimate of half a kilogram is correct. I 
did not try to come up with a new feather strength estimate in my reply 
because I did not have any Confuciusornis specimens to check out the N&D shaft 
diameter measurement which I -- correctly as Z et al proved -- did not trust. 
And I am suspicious about the N&D method in any case because it may not take 
feather overlap co-bracing into sufficient account. I will not do the 
calculations using my correct mass and Z et al's correct shaft diameters 
because I 
have no plans to further work on the issue at this time there being lots of 
other things on my plate, and others will certainly do it and what's wrong 
with that. 

GSPaul </HTML>