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Re: Avian flight stroke origin



Agreed on all points, sir, except to say that tinamous and turkeys
probably roost in trees more often than not, especially when they are
brooding chicks, rather than just occasionally.

I was persuaded by two different studies - one of them was Hopson, 2001,  
that Archaeopteryx and other early paravians had the foot anatomy of birds
that divided their time between foraging on the ground and in trees. I
wouldn't say the arboreal hypothesis is supported.



> Jason Brougham <jaseb@amnh.org> wrote:
>
>> My apologies for being unclear. I did not mean that Archaeopteryx may
>> have
>> stood in a tree like Penelope in that it would grip the tree with its
>> halluces. I meant that it would stand upright, without aid of hand
>> claws.
>
>
> Yes, _Archaeopteryx_ may have stood in trees.  My argument is that
> there is nothing in the anatomy that says it did so - at least not
> habitually.  _Archaeopteryx_ might indeed have had an ecology similar
> to a turkey (aside from the flight capabilities).  But turkeys are
> fundamentally terrestrial birds, even though they occasionally venture
> into trees.
>
>
>> However, on the point of halluces I still do believe that animals
>> without
>> halluces, and galliform birds with poor perching ability, still do quite
>> well in trees and roost in them routinely.
>>
>> In the wild turkey Meleagris, climbing in trees can be accomplished
>> without use of a gripping hallux. In the image below we see a wild
>> turkey
>> climbing a narrow branch to reach fruit, and both halluces are free and
>> not gripping anything:
>>
>> http://www.flickr.com/photos/jrnikon/3240582435/sizes/l/in/photostream/
>
>
> Sure, turkeys do okay in trees... But turkeys don't spend much time in
> trees, whereas other gallinaceous birds do, such as the cracids.  In
> phasianids, the proportions of the first digit vary according to how
> terrestrial/arboreal the bird is.  Turkeys (meleagridids) feed and
> nest on the ground, and the first digit is quite elevated, due largely
> to the shortened metatarsal I.  Nevertheless, the hallux of turkeys is
> still reversed, and capable of some opposability.
>
>
> An animal that spends much of its time in trees will acquire or retain
> arboreal adaptations.  In the case of terrestrial gallinaceous birds
> like turkeys, the hallux appears to have been secondarily elevated.
>
>
> Certain birds can still sit or roost in trees even without a perching
> foot.  Cormorants can, using their totipalmate feet - the anterior
> digits wrap over the branch, the same way they do a rock.  But
> cormorants are not in any sense arboreal.  Certain tinamous can roost
> in trees - but they don't actually perch, but sit on their tarsi using
> highly modified scales on the plantar tarsal surface.  Again, tinamous
> are not in any sense arboreal.
>
>
>> Goats, as we know, also climb trees without benefit of a hallux:
>>
>> http://www.odditycentral.com/videos/the-tree-goats-of-morocco.html
>
>
> Ah, I wondered when we'd get to "But goats can climb trees!"  :-)
>
>
> What we have here is the distinction between "capable of" and "adapted
> for".  At any given time on planet Earth, the vast majority of goats
> are not climbing trees, and have no desire to.  Just because an animal
> *can* climb a tree under certain circumstances does not make it
> arboreal.  Goats are *not* adapted for an arboreal lifestyle.
>
>
>
>
>
> Cheers
>
> Tim
>


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