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Re: 11th specimen of Archaeopteryx
> I never said they were. But the proponents of the arboreal lifestyle> are the
> only ones with a wealth of studies and research on their side.
Oh yeah? Which studies are those? All they do is cite existing
studies that show that feathers themselves are expensive to produce
(true) and that asymmetrical feathers have certain certain aerodynamic
properties (e.g. drag reduction) that would be consistent with
gliding. Nothing in their papers provides evidence linking those
self-evident claims to an arboreal lifestyle. Feduccia did try to
link claw proportions to an arboreal lifestyle, but the toe claws are
not actually consistent with arboreal birds (and appear to be
consistent with raptorial claws).
To put it bluntly, the BANDits generally use a rhetorical trick rather
than any data when they try to link asymmetrical wings to arboreality;
they create a false dichotomy between ground up and trees down, they
follow it with the arguement that flight in general should be "easier"
to evolve from trees since gravity can take the role of thrust
generation, and that's literally all they have. No note of the fact
that gliding isn't the only aerodynamic thing that can be done with
your wings, or that trees aren't the only place you can glide from.
Given the lack of any arboreal features in Archaeopteryx and related
taxa the issue of where it's "easier" to evolve flight isn't really
relevant (and furthermore, work by Mike Habib and others have shown
that in point of fact strong leaps - whether from trees or the ground
- and therefore thrust generation from the takeoff substrate are
actually the norm for birds, not a reliance on gravity for
Until there is even a single study that functionally links
asymmetrical feathers to arboreality, people _should_ discount it as
an arboreal feature.
>> If Archie had symmetrical feathers but a reversed hallux, it would be just
>> as easy to say that the hallux is not an arboreal feature and that it would
>> be possible to think up alternate uses for it, so therefore Archie has no
>> arboreal features.<<
Absolutely, if the hallux was still has high as it is in the current
fossil, and if the claws, flexor tubercles, and pedal anatomy and
proportions were still more consistent with a terrestrial lifestyle
(as they are in the actual fossil) then it would still be inconsistent
to argue for an aboreal lifestyle. Feather asymmetry or the lack
thereof has no bearing on where they lived, as it simply has no
functional correlation with either ecospace. There's no reason an
animal with symmetrical feathers couldn't live in trees nor a reason
why animals with asymmetrical feathers can't life on the ground, so
such hypotheses have to live and die on the actual anatomical
evidence. And for Archaeopteryx it's just not even close: it does not
look anything like an animal that perches or scampers around in trees.
On Mon, Oct 24, 2011 at 1:31 PM, Matthew Martyniuk <email@example.com> wrote:
> (meant to send this to the list...)
> Sure, some things are more uncertain than others. But which of these
> hypotheses concerning the possible asymmetrical remige functionality
> is currently better supported by evidence?
> 1) Lift generation for arboreal assistance (WAIR, or something similar)
> 2) Aiding in turning while running
> How many studies have been done on the role of asymmetry in each function?
> Scott Hartman wrote:
> "And finally, asymmetrical feathers are in no way directly linked to an
> arboreal lifestyle."
> I never said they were. But the proponents of the arboreal lifestyle
> are the only ones with a wealth of studies and research on their side.
> There are plenty of papers discussing WAIR. I'd be curious to read
> those for turning, especially since in modern birds, even those that
> use their wings for turning, the feathers are not aerodynamic, and
> there was apparently no selective pressure to retain asymmetry for
> this purpose. If we're doing science, when there are two competing
> hypotheses, one backed up by current studies (WAIR) and one not
> (turning), the response should not be "well, we have no idea what they
> were for." The response should be "current research suggests WAIR is a
> likely use for asymmetrical feathers while alternate hypotheses
> require more investigation."
> As Mike said above, there is no evidence to suggest that asymmetry was
> the ancestral condition, and in fact there's evidence against it
> unless you consider caudipterids and Sinornithosaurus to be
> secondarily flightless.
> What gets me is that people keep citing "lack of arboreal features",
> while discounting feather asymmetry as one, despite the fact that no
> alternate interpretations of that character have been seriously
> investigated. If Archie had symmetrical feathers but a reversed
> hallux, it would be just as easy to say that the hallux is not an
> arboreal feature and that it would be possible to think up alternate
> uses for it, so therefore Archie has no arboreal features. "The
> asymmetry is not an arboreal feature because Archie has no other
> arboreal features" does not strike me as a very sound
> On Mon, Oct 24, 2011 at 1:54 PM, Mike Keesey <firstname.lastname@example.org> wrote:
>> On Mon, Oct 24, 2011 at 10:51 AM, Matthew Martyniuk <email@example.com>
>>> We need to learn a lesson from the BANDits; it's not enough to shoot
>>> down a hypothesis without proposing any alternative.
>> On the other hand, there are cases where we have to admit, "We don't
>> know [yet]."
>> T. Michael Keesey
Scientific Advisor/Technical Illustrator