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Re: 11th specimen of Archaeopteryx



> 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.

It may not be necessary to have all of these adaptations, but
Archaeopteryx doesn't have _any_ of them.  The foot is simply the
opposite of what we would expect of a bird-like animal that lived in
trees.  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.

-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/