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Re: Science feather strength debate



Jason Brougham <jaseb@amnh.org> wrote:

> Yet, here is where I would caution all of us about drawing a priori
> conclusions based on morphology alone. Sometimes our logic alone can be
> too facile. If we knew modern day turkeys and tinamous only from fossil
> skeletons we might never guess that they roost in trees. All are
> anisodactyl. In turkeys Mt 1 is quite proximal, and the halluces don't
> quite reach the foot pads. In tinamous the halluces can be extremely tiny,
> medially positioned, and proximal (elevated), or even absent in some
> genera.


Those tinamous that roost in trees (i.e., certain species of the genus
_Tinamus_) do not use their toes to grasp branches.  Instead, they use
highly modified scales on the plantar surface of the tarsus to help
the distal hindlimb cling to a horizontal branch.  So these tinamous
don't actually perch, but sit on their tarsi.  This would appear to be
a highly specialized adaptation for roosting, and might represent a
way of bypassing the hallux's inability to be used for perching.


As for the turkey, it's my understanding that most if not all
phasianids have a hallux that is sufficient to oppose the other three
pedal digits.  Although the hallux of phasianids is certainly more
elevated than seen in cracids (for example), it is certainly
positioned well back on the foot - unlike any basal paravian
(including basal birds).


> None of this should be thought of as evidence that small troodontids or
> basal paravians climbed trees or shrubs, it just makes me wary about
> saying that they couldn't.


I'm not saying that they couldn't.  But I would say that if
troodontids, microraptorines, _Archaeopteryx_or any other basal
paravian climbed trees they did so in a manner that was very different
to any extant bird.


Cheers

Tim