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RE: Digit - loss - 5 finger fliers - stiff tails

Tracy Ford wrote:

One of the major problems with people in trying to understand arboreality is
that the only arboreal animals they are thinking of are like lizards or
small five toed animals and that only they could be arboreal. Who are we to
say animals like dromaeosaurids couldnt climb because they couldnt climb
like a lizard? Why?

Look at monkey. Do they always hug a tree when they climb? Do they
sometimes hold their body away from the trunk and climb?
We have to start opening our minds to other ways of climbing. And its not
just one thing for flight to have started. It is dozens of things that the
animal had to change/evolve for flight. Climbing is one of them. Holding the
body away from the trunk and climbing is another. Not impossible.

Exactly!  Couldn't have said it better myself.

Primates have a LOT to tell us about early avian evolution. Alan Feduccia is right in asserting that leaping sifakas might be a good analog for leaping & gliding proavians. However, unlike Feduccia we don't have to invent some imaginary post-_Longisquama_ pre-_Archaeopteryx_ "pseudosuchian" intermediate. Small deinonychosaurs like _Microraptor_ and _Sinornithosaurus_ fit the bill quite well.

George wrote:

Early dinobirds had five loci for airfoils on their body: the tail and the
four limbs. The first of these to develop an airfoil function must have been
the tail, mainly because it's simply the part that needs the least
modification to become one: just grow a fringe of feathers and voila.

I would say that proavians had only three such loci - two forelimbs and tail - and the feathers were modified on the arms and tail concurrently. There is no evidence that the hindlimbs were ever involved in the generation of an airfoil.

The forelimbs would naturally
have served to arrest the animal at the end of a leap, so there would be a
tendency to retain/improve the grasping function for this new role.




Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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