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Jonathan R. Wagner wrote:
>         Arborality may also explain the sickle claw of dromaeosaurs
> (climbing peton), the reversed hallux (even though it may not have been
> useful in perching per se), the highly mobile base of the tail (Dr. Holtz
> has commented on the difficulty of climbing a telephone pole with a
> broomstick up your butt) as well as the distal tail's rigidity (bipedal
> animals balancing on branches might appreciate a dynamic stabilizer as much
> or more than agile cursors). Indeed, Dr. James Norton and I have both
> proposed (on this list) various scenarios involving the role of trees in the
> dromaeosaur attack strategy (at least ancestrally) leading to fluttering 
> flight.

This is all starting to sound very familiar. I've been making exactly
these sort of speculations for years about Dromaeosaurs, flight, 
arboriality, etc. And I'm on the lowered end of the amateur scale -
just imagine what someone who knew what they were talking about
could do as regards providing actual proof!  :)

A small section on Unenlagia has been kicking about at my Geocities
website for quite a while. Basically I suggest that the avian-style
glenoid cavity, with the ability to raise the arms up high, would
be useful for an arboreal creature. Such a life style would also
require well-muscled forelimbs, and perhaps some sort of reinforcing
in the shoulder area (furculas?). Sickle-claws on the feet may
also be useful, not just for climbing but as wounding/killing
instruments that could be driven into large prey from above when
leapt on from a height. So our hypothetical ancestor has strong
forelimbs, flexible glenoid sockets, perhaps a covering of insulatory/
display feathers, and a tendancy to perform controlled falls from
high places. Is it such a huge leap (pun intended) from this to
powered flight? 
        Just imagine feathered, highly mobile forelimbs that,
along with mobile (and perhaps also feathered) tails, are used to
balance the creature while free-falling onto prey to keep the predator
in an upright position (just as people may pin-wheel their arms as they
fall to do the same thing). What springs to mind is a mouse climbing
across something narrow, swinging its tail about to maintain its
balance - only a bipedal creature could also use its forelimbs.

Any and all criticisms will be much appreciated. Let the flaming
commence.  :)
        Dann Pigdon
        Melbourne, Australia

        Dinosaur Reconstructions:
        Australian Dinosaurs: