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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?

Ronald Orenstein 
1825 Shady Creek Court
Mississauga, ON
Canada L5L 3W2

On 2010-11-12, at 9:01 AM, "Jason Brougham" <jaseb@amnh.org> wrote:

> Mike,
> 
> 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.
> 
> -Jason
> 
>> 
>>> 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.>
>> 
>> 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).
>> 
>> Cheers,
>> 
>> --Mike H.
>> 
>> 
>> 
> 
> 
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
> 81st Street at Central Park West
> 212 496 3544
> jaseb@amnh.org
>