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arboreality in dinosaurs

I like the way the current discussion is going regarding arboreality in
dinosaurs.  Accepting a range of degrees of arboreality, from occasional
to frequent to exclusively, reduces the polarity in the "trees-down" vs
"ground-up" debate and opens the door to some new and interesting
scenarios.  It seems logical to me that a small feathered biped that spent
some time in the trees or bushes would have developed a means of
predation that utilized the height advantage (for example, pouncing) and
would also have developed a means of getting into and out of the trees
quickly (for example, flight).

With respect to point of separation between protobirds and
dromaeosaurs, I would place it before the development of the relatively
rigid tail seen in the larger theropods.  If anything has troubled me about
the arboreal origin of birds from a theropod ancestor, it has been the tail. 
A stiff tail, even with some proximal flexibility, just doesn't seem
conducive to getting around in the trees, especially in dense branching
situations.  A flexible tail, which Acheopteryx seems to have, would
seem a requirement.



James M. Norton, Ph.D.
University of New England
11 Hill's Beach Road
Biddeford, ME  04005
phone: [207]283-0171 x2270
fax: [207]283-3249
email: jnorton@mailbox.une.edu