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Re: Fwd: Science feather strength debate



On 11/4/2010 10:46 AM, Jason Brougham wrote:

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.

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.

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.

Individual D. melanogaster can vary *way* more than 20% in lab (starved vs overfed), and fly quite well at both ends of the range. As birds are larger than flies, the mass variation w/in individuals is relatively smaller, but still -- any mass measurement must include more than a simple number to be meaningful relative to aerodynamic considerations. Maximum, minimum, median and daily average mass are all useful concepts according to need.

I have formed the rather simplistic opinion that in the controversy at hand, one side has taken the maximum and the other side has taken the minimum.

Even when specified as such, I do not think that giving a mass estimate that is maximal (as much as the animal *could* have weighed) is very useful in determining whether it could viably fly, in the ecological sense. Is it unknown in extant birds that individuals temporarily cannot fly when they eat too much?

I personally would give more credence to GSP's mass estimate as a result.

In any case, what the mass estimation or measurement given is meant to represent (max, min, and\or average) is critical information when considering volant animals, and sometimes not supplied.