Re: Feathered Dragons: Studies on the Transition from Dinosaurs to Birds

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<Oh yes -- but the position of mt I, namely at the distal end of the
metatarsus, and the great length of its toe are pretty convincing.>

  Convincing of what? What is the mechanical advantage of the metatarsal
1, not preserved in *Epidendrosaurus* being located distally? For that
matter, why would the hallux be "non-reversed"/heterodactyl if it was an
opposable digit? Two many unknowns for that matter to be "unequivocal," as
you put it. One may be convinced, but the data is rather equivocal with
the two known specimens preserving opposite orientations from one another.
With large feet and a distally placed first digit, one can also assume
there was a weight-distribution advantage, and that can have lots of
benefits in a wet, soggy environment such as a lake shore in a wooded
area, or a marshy one, as one sees in small segnosaurs in the area
(*Beipiaosaurus*) and numerous "prosauropods". The argument here is
equivocality.
 
<:-) That's what I mean. It makes an arboreal lifestyle rather
improbable.>

  No, it doesn't. It means limb grasping is excluded as a means of
locomotion. This is different. Neither sloths nor brachiating apes use an
opposable digit when locomoting, but do this effectively well simply
because a thumb or everted hallux is unncessecary. No, I am not implying
brachiating feet in scansoriopterygids, but using this as a method by
which many chiefly arboreal animals manage without a reversed hallux.
Chickens and waterfowl still manage to perch without an engaging hallux,
so that's not neccessarily a bonus, but seems to be an advantage to
perching in general; wood ducks not only live in trees, but nest there
with their young, another lifestyle without perching adaptations or branch
grasping ones. There's more ... cats ... animals can climb without using
trees, such as rocks, and still don't need opposable digits, as in
mountain goats....

  Improbable? I think not.

  Cheers,


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
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