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Convergent flight mechanisms? (was Re: Protoavis)



Larry Febo wrote:
> 
> I think that all these features were flight related. I`ve been thinking more
> and more about the "Advanced Mesotarsal" ankle and I think that this (which
> limits motion to a simple hinge, not allowing a "twisting" of the foot),
> along with fused metatarsals, and elongation of the metatarsals, are all an
> adaptation for "leaping". 

It would be interesting to compare the ankle joints of tarsiers
("bush-babies"). They are phenominal leapers, and supposably have the
largest relative tarsals of any extant animal. Have their ankles
been simplified in this manner?

>I think this ankle developed in conjunction with
> the advanced shoulder girdle, acrocoracoid process, and flapping flight. A
> bird, or pterosaur would have to leap free of the branch it was perched on
> to not damage its wings when it takes flight.

Many modern birds don't perch (at least not very well), and manage to
take off from ground level even when it is an extremely difficult
process (as in albatross). I wouldn't think that pterosaurs were
in much of a position to leap from a branch, especially since their
hind limbs tend to have a sprawling articulation. Pterosaur bipedalism
(my opinion, and that of others) was probably similar to that of
some lizards (frilled dragons, Jesus lizards). Enough for a short,
semi-upright sprint, but not for prolonged running. Do modern
dragon lizards and the like have any decent leaping capabilities?

> SNIP

> When you talk about birds and pterosaurs, ...people always bring up Bats! I
> hate to group the three. Birds and Pterosaurs are OBVIOUSLY much closer than
> either is to bats.......(that`s how I feel about it). Comparisons can only
> be made on vaguely similar
> physical mechanics, I`d just as soon leave them out of the equation
> alltogether!
>

And yet bats and flying foxes seem to be more similar than birds are
to pterosaurs, and there is good evidence that the former are not
closely related (flying foxes perhaps being closer to primates). If
this is the case (and I suspect it is) then flight must have evolved
at least twice amongst mammals, perhaps making the evolution of flight
not as rare as some people think.

(Incidentally, I have a large fig tree in my back yard that is 
frequented by flying foxes at the moment. They are truely remarkable
creatures to watch. Thankfully they only visit one or two at a time.
I'd hate to have an entire colony anywhere nearbye.)
 
-- 
____________________________________________________
        Dann Pigdon
        GIS Archaeologist
        Melbourne, Australia

        Australian Dinosaurs:
        http://www.geocities.com/capecanaveral/4459/
        http://www.alphalink.com.au/~dannj
____________________________________________________