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Re: Adaptive advantage (was Re: ABSRD BAND on Sinornithosaurus feathers)





Ronald Orenstein wrote:

At 09:14 AM 16/03/01 +0000, Scott Hartman wrote:
Theropods are the anti-scansors.  Their limb proportions and acetabular
articulation precludes this type of lifestyle.  [snip]

I have been pointing out for some time now on this list that this simply is
not true.  There are living birds that are excellent climbers without
having to resort to flight to help them do it - even if you leave aside
specialized trunk-foragers like woodpeckers.

Agreed. There are claws which, based on their morphology, are specialized for climbing trees. Birds with this type of claw do indeed climb trees. However, it does not follow that this type of claw is essential for tree-climbing. Birds *without* claws of this type are still able to climb trees.


The shape of the claws in _Archaeopteryx_ suggest that it did use its claws to climb trees (Yalden, 1985; Feduccia, 1993). This does not mean that small maniraptoran theropods which did *not* have specialized scansorial claws were incapable of climbing trees.

My preferred model for the origin of flight does not claim that small maniraptorans were specialized scansors. They climbed trees when it suited them. All prey capture (including after they had leaped down from trees) occurred on the ground. Hence the retention of long legs and other features ill-adapted for scansoriality.


I see no reason why a long-legged theropod could not have done the same
thing, if perhaps less efficiently - and remember that even though they
lacked wings, they could use arms and mouth to grip limbs if necessary.

Exactly. The long arms, large hands, mobile wrists, and sharp claws (on both hands and feet) may have served adequately (but certainly not perfectly) in getting these predators up tree trunks. Small size would help too (_Archaeopteryx_-size, or lower). Chatterjee has suggested that the stiff tail was used as a brace during trunk-climbing - this I'm a little more skeptical of.



Tim

------------------------------------------------------------

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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