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Climbiing Dinosaurs (RE: a little background)



Jaime,

I agree with Tim Williams.  It is a nice naturalistic rendering of a
climbing dromaeosaur!
Just to confirm, are you saying that the position and orientation of the
forelimb in the illustration represents the farthest forward (cranial)
excursion the humerus can make without being separated from its' contact
with the glenoid?

I've been discussing the idea of tree climbing in dromaeosaurs with Bob
Bakker recently ( we're working on a book together).  It seems to me that in
combination, the plane of the ungual on pedal digit two ( offset medially )
for that modified "climbing lumberjack" movement, along with retroverted
pubes (reorientation of attachment for hindlimb adductors) and large cnemial
crest for leg extension, can be viewed as much as an adaptation for climbing
as it can be as an organ for dispatching prey or weapon of defense.

One of the arguments some individuals at last SVP were making against tree
climbing was, of course, that if the animal attempts to retract the humerus
(in pulling its body upward), that the mechanics of the forelimb want to
force the arm to "collapse" as it is designed to do, which would then negate
its ability to move upward.  As you rightly point out, what may be more
important here is that the arms in extension remain in a relatively static
position, simply supporting the body weight AFTER the legs have thrust the
body upward ( and while the legs are then drawn up under the body for the
next thrust upward ). So really then, all the work in tree climbing
dromaeosaurs is done through leg propulsion with the arms and tail
secondarily helping in manoeverability, in more lateral movements onto tree
limbs, etc...  The only thing that appears to me to be slightly problematic
is moving its body and tail through more densely limbed conifers, if they
attempted that.  I strongly suspect however, that even that was possible, as
I'm sure dinosaurs were as capable in their own environments as most modern
vertebrates are in theirs today.

Mike Skrepnick