This requires that the "sickle claw" gave any sort of benefit to keeping
an animal upright when it stood on a branch -- or, more accurately, kept
the animal upright while _sleeping_ on a perch. The latter is achieved in
modern birds by a specialized tendon that connects to the hallux that
"locks" the digit in place. The foreward toes are wrapped around the
front, the back toe wraps around back, and the animal stays on the branch
without falling off while it sleeps. This is "perching."
It is probably very inappropriate to term "sitting in a tree" as
"perching," although the term is so casually used for normative in-tree
behavior (monkeys "perching," humans "perched" atop a thing) due to a
lackadaisical way of associating terms with position without any recourse
to their anatomical meaning. You get this in fiction [genre] a lot, where
terms are "adapted" to suit the use of some sense the author wants to
apply, without actually understanding the term.
If a dromaeosaur or any sort of non-avialaean theropod without such a
tendon-locking mechanism were to try to sit in a tree, it might find
itself with the problem of trying to sty upright when falling asleep. This
doesn't impair _climbing_, but it does any other sort of behavior.
Nesting, squatting, or whatever else without having to sit on a branch is
fine, but that means one must be more selective about your "perch," and
cannot just climb into a bush.
Cheers,
Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a
Billion Backs)
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Date: Fri, 4 Nov 2011 17:43:03 +0000
From: ssselberg@hotmail.com
To: dinosaur@usc.edu
Subject: Re: 11th specimen of Archaeopteryx
Isn't it possible that the sickle claw could have allowed basal
deinonychosaurs to perch?
If so, wouldn't that have made a reversed hallux redundant, and also
allowed the third and fourth
toes to retain their more corsorial proportions? Or perhaps these animals
were more in the habit of
clinging to tree trunks than perching?
I think that the reason so many people put some maniraptors in trees
(besides the "if it looks like a duck..." intuitive sense of it) is that
it's hard to believe that animals as adaptable they appear to be would
NOT have invaded the canopy when so many others have. If snakes and frogs
existed only as fossils, would anyone be postulating tree-snakes and
tree-frogs? And even if I'm wrong about the sickle claw and perching,
aren't fossils of arboreal creatures very rare, making it possible that
most of the fossils we have found were the more terrestrial species of
what may have been more arboreal groups?
Scott Selberg