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RE: 11th specimen of Archaeopteryx‏



  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)


----------------------------------------
> 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
>