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Re: 11th specimen of Archaeopteryx



> Wouldn't it be more accurate to say that studies on the toes of> 
> Archaeopteryx and Microraptor have mixed results?

Sure...but not equally so.  By the way, let me say that I am totally
excluding Microraptor from this discussion.  Not because it isn't
fascinating in its own right, but because I don't believe that
Archaeopteryx and Microraptor are necessarily doing the same thing.

> Also, please note, I'm not advocating an arboreal lifestyle. I've only
> looked to roosting, like we see today in many ground - based birds, as one
> hypothetical model for the origins of arboreality in paravians.

The thing about roosting is it requires that the birds be able to land
at a slower speed without stalling.  There's not evidence that
Archaeopteryx could do this, and it's limb proportions and pedal
morphology show no adaptations to overcoming the much higher landing
speed (missing branches is not a good way to...errr...fly).  Of course
once WAIRing was possible you could have roosting even without flight,
but as others have stated that probably does not include
Archaeopteryx.  I'm not totally sold on Microraptor either way, but
then I'm also not considering it at the moment.

That said, I'm not totally opposed to roosting as an origin of
arboreality in paravians, I just think it can't be applied to
Archaeopteryx.  And as I've argued previously on the list, I think the
only reason Archaeopteryx even shows up in these discussions is due to
the mistake of referring to it as a "bird", not because anything in
its anatomy supports it.

> Forgive me if you have already refuted these sources, and I know that one
> recent paper did contradict them, but allow me to mention two examples
> from the literature:
>
>  Hopson (2001) found that Archaeopteryx had toe proportions that fell in
> the overlap between terrestrial and arboreal birds, with those which
> forage on the ground.

Hopson explicitly finds that Archaeopteryx has pedal proportions
consistent with extant terrestrial birds.  If I may quote the
conclusion: "Archaeopteryx has pedal phalangeal and hind limb
proportions that overlap those of the least cursorial terrestrial
modern birds."

The pelvic morphology and other aspects of the anatomy agree with
Hopson's conclusion that Archaeopteryx doesn't seem to be particularly
specialized as a cursor.  None-the-less, nothing in its pedal
morphology is found to be suggestive of an arboreal lifestyle.  I
realize that he also concludes that Archaeopteryx and Confuciusornis
"were probably equally at home foraging on the ground or in the
trees", but we're already running into problems when equating those
two taxa into the same lifestyle, and in large part this is based on
concluding that they have "unspecialized feet" with hands that "were
specialized for grasping".  Unfortunately, it's not at all clear that
Archaeopteryx was capable of flight (at least in the sense of "let's
head up to a tree branch and land there"), and the grasping hands have
clear potential for use elsewhere (e.g. you could argue for
arboreality in Utahraptor based on the same line of reasoning).

> Glen and Bennet (2007) studied toe claw curvature and found that the
> values for some specimens of both Microraptor and Archaeopteryx fell in
> the ground foraging (exemplified by pigeons and doves) range while others
> were in the ground - based range.

I must have a different copy of their paper than you do, as they
explicitly conclude "Our findings suggest early birds foraged
predominantly on the ground, rather than supporting previous
suggestions of arboreal claw adaptations, which appear to have evolved
later in the lineage."

Which is of course my point.

Best,

-Scott
On Wed, Nov 2, 2011 at 12:23 AM, Jason Brougham <jaseb@amnh.org> wrote:
> Scott Hartman wrote:
>
>>In the absence of any other supporting data it's just special
>> pleading to keep trying to explain away the foot anatomy as somehow
>> "not preventing" an arboreal lifestyle.
>
> Wouldn't it be more accurate to say that studies on the toes of
> Archaeopteryx and Microraptor have mixed results?
>
> Also, please note, I'm not advocating an arboreal lifestyle. I've only
> looked to roosting, like we see today in many ground - based birds, as one
> hypothetical model for the origins of arboreality in paravians.
>
> Forgive me if you have already refuted these sources, and I know that one
> recent paper did contradict them, but allow me to mention two examples
> from the literature:
>
>  Hopson (2001) found that Archaeopteryx had toe proportions that fell in
> the overlap between terrestrial and arboreal birds, with those which
> forage on the ground.
>
> Glen and Bennet (2007) studied toe claw curvature and found that the
> values for some specimens of both Microraptor and Archaeopteryx fell in
> the ground foraging (exemplified by pigeons and doves) range while others
> were in the ground - based range.
>
>
>
>>> Not to pounce on this one sentence, but I simply don't agree that this
>>> is> how evolution works. There are myriad cases where we might expect
>>> an> anatomical adaptation, where one would make sense, but we do not get
>>> one.> It is not true that there must be an "excuse".
>>
>> Sure, but we also have to let the evidence drive our inferences, not
>> the other way around.  Not only is the hallux of Archaeopteryx too
>> high and not reversed, but none of the toe claws have the tubercle
>> morphology seen in perching birds, the toe proportion do not match
>> perching birds, and there is no ventral curvature in the pedal
>> phalanges as seen in perching birds.
>>
>
>>
>> -Scott
>> On Tue, Nov 1, 2011 at 11:35 PM, Jason Brougham <jaseb@amnh.org> wrote:
>>> Tim Williams wrote:
>>>>
>>>> If _Archaeopteryx_, microraptorines etc were roosting in trees,
>>>> there's simply no excuse for *not* having a hallux that was low enough
>>>> and large enough to grip branches - ideally combined with at least
>>>> some reversal of the hallux, for the pes to be capable of some kind of
>>>> opposable grip.
>>>
>>> Not to pounce on this one sentence, but I simply don't agree that this
>>> is
>>> how evolution works. There are myriad cases where we might expect an
>>> anatomical adaptation, where one would make sense, but we do not get
>>> one.
>>> It is not true that there must be an "excuse".
>>>
>>> just as one quick and pedestrian example, there is no "excuse" for
>>> mammals
>>> to have external testis which descend into a scrotum seeking the lower
>>> temperatures that provide more efficient spermatogenesis. Birds adapted
>>> to
>>> endothermy and were able to keep their testis inside the abdomen, where
>>> they are far less prone to injury.
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>> --
>> Scott Hartman
>> Scientific Advisor/Technical Illustrator
>> (307) 921-9750
>> website: www.skeletaldrawing.com
>> blog: http://skeletaldrawing.blogspot.com/
>>
>
>
> 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
>
>



-- 
Scott Hartman
Scientific Advisor/Technical Illustrator
(307) 921-9750
website: www.skeletaldrawing.com
blog: http://skeletaldrawing.blogspot.com/