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Re: Science feather strength debate
I have always wondered whether a bird like the chachalaca might be a good model
for the way Archaeopteryx got around. Has anyone ever used cracids for these
sort of comparative purposes?
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On 2010-11-12, at 9:01 AM, "Jason Brougham" <firstname.lastname@example.org> wrote:
> That is most interesting. I was not aware that the humeral strength of
> grebes overlapped with the most basal birds. I wonder how Confuciusornis
> would fare using that same metric.
> I also wonder if one measures the strength of the humerus by diameter, by
> wall thickness, by density, by putting specimens in a press or so on. I
> imagine it could be complicated. I've read that Rogers and LaBarbera
> (Journal of Zoology, 230, issue 3, pg. 433 1993) demonstrated that the
> density of trabeculae inside the pigeon humerus also affects mechanical
> strength. I ask because it is easy to snap a pigeon humerus in the lab,
> but not so easy to do with a fossil.
> By the way I completely concur that comparing Archaeopteryx to a
> hummingbird makes the former look radically underbuilt. I am keenly aware
> that the minimum requirements for flight are way lower, in fact that was
> the point I was trying to make, however poorly.
> I would like to see how the humerus of Geococcyx stacks up. Meinzer (The
> Roadrunner, 1993, Texas Tech U. Press) reports that they usually ascend to
> their nests in trees by leaping upward to a series of branches, and not by
> flying. I've been imagining similar behavior in an animal like Anchiornis
> or other small troodontids - with long legs and probably somewhat
> underpowered flight apparatus. One could imagine how an evolutionary
> feedback loop could be set up in an animal that is habitually leaping in
> and out of trees like this. And until I read Meinzer's report I never
> really imagined an animal the size of a roadrunner leaping eight feet into
> a tree. But now I can imagine these small, basal, paravians doing so.
> Perhaps the ancestral Paravian didn't need to be strictly arboreal before
> one or more lineages began to glide, they could have just been roosting or
> foraging part-time in trees.
>>> Moreover, we would both agree that 20% doesn't matter to extant
>>> birds with highly derived flight apparatus, but modern birds have a lot
>>> 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
>>> like any hypothetical ancestor of birds, 20% could be a crucial
>>> between ascending flight and gliding.>
>> One point worth mentioning here is that while some modern birds do indeed
>> execute high-load maneuvers, those that do also have stronger limbs than
>> those that do not. Peregrine falcons, for example, have humeri over 6
>> times stronger than those of an albatross, relative to body mass (i.e.
>> they can take 6+ times as many body weights of force). Therefore, one of
>> the key methodological points in comparing the structural strengths of
>> feathers or bones in living birds to fossil ones is to use relevant living
>> taxa - don't use hummingbirds and falcons as comparisons for
>> Archaeopteryx, for example. Doing so will inevitably make Archaeopteryx
>> look underbuilt. By contrast, something like a grebe, which is still
>> quite a derived and reasonable flyer, does not have limbs all that much
>> stronger than the most basal birds, relative to mass (I am using the
>> Yalden mass for Archie in that comparison).
>> --Mike H.
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
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